Technical Guide
How To | Configure IGMP for Multicasting on Managed Layer 3
Switches on AlliedWare Plus™
Introduction
Allied Telesis routers and managed Layer 3 switches use IGMP—Internet Group Management
Protocol—to track which multicast groups their clients belong to. This enables them to send the
correct multimedia streams to the correct destinations.
This How To Note describes basic and advanced IGMP configuration, in the following major
sections:
C613-16176-00 REV A

an overview of IGMP and definitions of some of the IGMP terminology

examples and discussion of the most common IGMP functionality—IGMP snooping, IGMP
Querier behaviour and selection, and IGMP proxy

examples and discussion of the advanced functionality available through the feature-rich IGMP
implementation in Alliedware Plus

information for debugging

information about the STP state of the simple three-switch ring used in most examples

information about IGMPv3
alliedtelesis.com x
Introduction
Contents
Introduction .............................................................................................................................................................................1
Related How To Notes ...........................................................................................................................................4
Products and software versions this note applies to..............................................................................4
IGMP overview ....................................................................................................................................................................5
Queriers and Snoopers...........................................................................................................................................5
Messages ..........................................................................................................................................................................6
Choosing group addresses ....................................................................................................................................6
IGMP snooping ......................................................................................................................................................................8
Explanation of IGMP Snooping ...........................................................................................................................9
Configuration Example ......................................................................................................................................... 10
Using the show command output to investigate IGMP state......................................................... 13
Multiple potential IGMP Queriers........................................................................................................................... 16
Example ......................................................................................................................................................................... 17
Explanation of Multiple Potential IGMP Queriers................................................................................. 20
IGMP proxy .......................................................................................................................................................................... 24
Example ......................................................................................................................................................................... 25
Explanation of IGMP Proxy................................................................................................................................ 28
Multiple Proxies......................................................................................................................................................... 32
Query solicitation (rapid recovery from topology changes).................................................................... 34
How Query Solicitation works........................................................................................................................ 34
Why convergence takes so long without Query Solicitation......................................................... 35
Speeding up IGMP convergence in a non-looped topology........................................................... 41
Enabling Query Solicitation on multiple switches in a looped topology.................................. 41
IGMP filtering (controlling multicast distribution) ........................................................................................... 43
Example ......................................................................................................................................................................... 43
IGMP throttling (limiting the number of streams for each subscriber) .............................................. 45
Example ......................................................................................................................................................................... 46
Explanation of IGMP throttling......................................................................................................................... 49
Static IGMP ........................................................................................................................................................................... 50
Example ......................................................................................................................................................................... 51
Explanation of Static IGMP................................................................................................................................. 54
How clients leave groups: queries and timers.................................................................................................. 59
Overview of leave process................................................................................................................................. 59
Querier timer values.............................................................................................................................................. 60
Snooper timer values............................................................................................................................................. 61
Comparing the Querier and Snooper timers ......................................................................................... 62
Consequences for high-loss and high-lag networks............................................................................. 62
Page 2 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Introduction
IGMP Fast Leave.................................................................................................................................................................62
Example..........................................................................................................................................................................63
Explanation of IGMP Fast Leave ......................................................................................................................65
Immediate Leave and Fast Leave.....................................................................................................................68
Configurable IGMP timers and counters .............................................................................................................68
Timer and counter relationships......................................................................................................................69
Default values .............................................................................................................................................................70
Last Member Query Count and Last Member Query Interval ....................................................71
Robustness Variable ................................................................................................................................................73
Default Query Interval..........................................................................................................................................75
Max Query Response Interval..........................................................................................................................76
Group Membership Interval ..............................................................................................................................78
Example of bad choices for timer values .............................................................................................................78
Stopping Snoopers from snooping non-IGMP messages...........................................................................80
Example..........................................................................................................................................................................81
Controlling which addresses create All Groups entries.....................................................................85
IGMP debugging .................................................................................................................................................................86
Support for IGMPv3 ........................................................................................................................................................88
Benefits ...........................................................................................................................................................................89
Report suppression.................................................................................................................................................89
Source Address Check..........................................................................................................................................90
Tips for making an IGMP network more efficient ..........................................................................................90
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 3
Introduction
Related How To Notes
You also may find the following AlliedWare Plus How To Note useful:

How To Configure PIM on AlliedWare Plus
Products and software versions this note applies to
IGMP is available on all the following Allied Telesis managed Layer 3 switches running AlliedWare
Plus™:

x210 Series/switches (IGMP snooping only, not IGMP Querier)

x510 Series/switches

x600 Series switches

x610 Series switches

x900 Series switches

SwitchBlade® x908 switches

SwitchBlade® x8100 Series switches
For most examples in this How To Note, we used:

one x900 switch (AlliedWare Plus)

two x600 switches (AlliedWare Plus)

one AT-8824 switch (AlliedWare)

one PC running VLC media player as the multicast server (see www.videolan.org)

client PCs
Page 4 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP overview
IGMP overview
Clients in an IP subnetwork use IGMP to indicate that they
are interested in receiving a multicast stream. IGMP then
ensures that routers and switches forward multicast
packets out the appropriate ports to the interested clients.
IGMP is very flexible, as the examples in this How To
Note show, but the basic operation is simple. When a
client wants to start receiving a multicast—which is also
called joining a multicast group—the client sends an IGMP
Membership Report message. When a router or switch is
running IGMP and receives a Report message, it starts
forwarding traffic for the relevant multicast group to the
client.
IGMP periodically polls clients by sending General Query
messages, to check that the clients still belong to their
multicast groups.
To leave a group, a client sends an IGMP Leave message to
indicate that it no longer needs to receive the group traffic.
Note that IGMP does not exchange multicast routing
information between subnets. The multicast routing
protocol PIM does this.
Queriers and Snoopers
It is neither necessary nor desirable for every router or
switch in an IP subnetwork to coordinate multicast traffic
flows. Instead, a single router or switch does this and is
called the Querier or the Designated Router. The Querier
generates Query messages to check group membership,
and processes Membership Reports and Leave messages.
However, other routers and switches in the network need
to know whether to send multicasts out each of their
ports. They find out this information by becoming
Snoopers. Each Snooper checks IGMP messages before
forwarding them to and from the Querier, and uses the
information in the messages to determine which ports to
send multicasts out of.
The key differences between a network’s Querier and its
Snoopers are:

IGMP terms:
Multicast or Multicast stream
A flow of information—usually
video or audio—that can go
from one source to many
destination clients.
Group
A multicast stream that clients
can join. Groups have IP
addresses in the 224.0.0.0/4
network.
Group member
A client that belongs to a
particular multicast group.
IGMP Querier or Designated
Router
A device in a subnetwork that is
the coordinator for all multicast
streams and IGMP membership
information. Each subnetwork
has only one Querier (see
"Multiple potential IGMP
Queriers" on page 16). The
Querier generates Membership
Query messages to check which
clients are group members, and
processes Membership Reports
and Leave messages.
IGMP Snooper
A device that spies on IGMP
messages to create flow
efficiencies by ensuring that
multicast data streams are only
sent to interested ports. A
Snooper can decide on the best
path to send multicast packets at
Layer 2 but it cannot alter those
packets or generate its own
IGMP messages.
IGMP Proxy
A device that passes
membership reports upstream
and multicast streams and
queries downstream. The proxy
acts on behalf of clients and
servers by altering packets.
The Querier generates Query messages to find out
which ports need to transmit each multicast stream.
The Snoopers also use Query messages to find this
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 5
IGMP overview
out, but they do this by passing on the Querier’s messages—Snoopers cannot create Query
messages themselves.

The Querier has IGMP enabled as part of its IP configuration. Snoopers do not require any
configuration because snooping is enabled by default on Allied Telesis routers and managed
Layer 3 switches.

Querying is a Layer 3 feature—the Querier looks into the IP headers of packets to determine
whether to forward them. IGMP snooping is a Layer 2 feature. It does not require an IP
configuration.
Messages
The following table describes the different IGMP messages in more detail.
IGMP message types:
Membership Report
A client sends this when it wants to receive a multicast group. The Membership Report (sometimes
called a join) is essentially a message that declares an interest in listening to a specified group.
Leave
A client sends this when it wants to leave a group.
General Query
The Querier sends this to all clients—whether or not the Querier is currently sending multicasts to
the client—to find out which groups they are listening to. Responses to General Queries ensure that
the Querier’s group membership information stays up to date.
The group address field for General Queries is set to 0.0.0.0. They are sent to a destination address
of 224.0.0.1, and by default Allied Telesis routers send them every 125 seconds.
Specific Query
The Querier sends this to a group address, to check whether clients are still listening to that group.
The Querier sends a Specific Query after a client sends a Leave message for that group. Specific
Queries enable the Querier to confirm when all downstream clients have left a group, so that the
Querier can stop sending the multicast stream.
Membership Query
This is a general term for both Specific and General Queries.
Query Solicit
Switches send this when STP or EPSR detects a topology change. The Querier responds by sending
a General Query immediately instead of waiting until groups time out. This remaps IGMP to the new
topology as quickly as possible.
Choosing group addresses
This section describes things you need to be aware of when choosing addresses for your
multicast groups.
Reserved IP addresses
IP addresses in the range 224.0.0.0-239.255.255.255 are multicast addresses, but many addresses
in this range are reserved. Therefore, before choosing a multicast address, you should check its
status in the “Internet Multicast Addresses” document at the IANA website at www.iana.org/
assignments/multicast-addresses.
Page 6 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP overview
IPs using the same MAC
Another complication is that multicasting is designed to use each packet’s group IP address to
determine a multicast MAC address to send the packet to. However, multicasting does not have
a 1:1 mapping of IP address to MAC address—instead each multicast MAC address corresponds
to 32 multicast IP addresses. This means that different multicast IP addresses use the same MAC
address.
The MAC address only uses the last 23 bits of the IP address; it ignores the IP’s first octet and
the first bit of the second octet. Note that all IP multicast MAC addresses start with 01-00-5E.
You need to avoid using multiple IP addresses that have the same MAC address. In practice, this
means that if you use x.0.y.z, then do not use x.128.y.z (or vice versa), where x is anything from
224-239, and y and z are the same in each IP address. For example, if y=6 and z=200 then these
IP addresses use the same MAC: 224.0.6.200, 224.128.6.200, 225.0.6.200, 225.128.6.200, and so
on.
To see this in detail, consider 224.0.6.200. This has a multicast MAC of 01-00-5E-00-06-C8, like
this:
IP address, decimal:
224.
IP address, binary:
11100000 00000000 00000110 11001000
0.
MAC address, binary:
MAC address, hex:
6.
200
0000000 00000110 11001000
01-00-5E -00
-06
-C8
Therefore, the following multicast IP addresses will all have the same MAC address as
224.0.6.200, because their last 23 bits are all the same:
IP address, decimal:
IP address, binary:
224.0.6.200
11100000 0
0000000 00000110 11001000
224.128.6.200
11100000 1
0000000 00000110 11001000
225.0.6.200
11100001 0
0000000 00000110 11001000
225.128.6.200
11100001 1
0000000 00000110 11001000
226.0.6.200
11100010 0
0000000 00000110 11001000
226.128.6.200
11100010 1
0000000 00000110 11001000
227.0.6.200
11100011 0
0000000 00000110 11001000
227.128.6.200
11100011 1
0000000 00000110 11001000
...
...
...
239.0.6.200
11101111 0
0000000 00000110 11001000
239.128.6.200
11101111 1
0000000 00000110 11001000
Different IPs
The same MAC
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 7
IGMP snooping
Avoid x.0.0.y, x.0.1.y, x.128.0.y, and x.128.1.y
It is particularly important to avoid using any address in the ranges x.0.0.y, x.128.0.y, x.0.1.y, or
x.128.1.y (where x is 224-239 and y is 1-254).
This is because x.0.0.y and x.128.0.y will map to the same multicast MAC address as 224.0.0.y.
Similarly, x.0.1.y and x.128.1.y will map to the same multicast MAC address as 224.0.1.y. Most
addresses in the ranges 224.0.0.y and 224.0.1.y are reserved for contacting all routers, or for
routing protocol messages, so they are always flooded out all ports in the relevant VLAN.
Therefore, all addresses in the ranges x.0.0.y, x.128.0.y, x.0.1.y, or x.128.1.y are flooded out every
port in the relevant VLAN. Using these addresses can significantly increase multicast traffic in
your network.
If you are debugging a situation where it seems that certain multicast groups are forwarded
when you think they shouldn’t be, check whether the choice of group addresses has violated any
of the recommendations above.
IGMP snooping
In the following example ("Configuration Example" on page 10), we discuss IGMP snooping, the
key to efficient multicast traffic flow in a layer 2 network. IGMP snooping is enabled by default on
switch ports in Allied Telesis managed Layer 3 switches and routers—it does not require any
configuration.
In a single-switch network, IGMP snooping makes multicasting happen with no configuration at
all. All you need to do is connect your server and clients to the switch.
In a multi-switch network, at least one switch must also have an IGMP configuration. This switch
is called the IGMP Querier and coordinates the flow of multicast information through the
network. The following example describes a multi-switch configuration, so as well as discussing
the effect of IGMP snooping, it outlines the actions that the Querier takes. "Multiple potential
IGMP Queriers" on page 16 discusses the role of the Querier in greater detail.
Page 8 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP snooping
Explanation of IGMP Snooping
This section steps through the events that occur in a typical use of multicasting in this network:
to stream multicast packets for a group. The following figure shows the process by which IGMP
tracks multicast clients and ensures that the correct clients receive the stream.
What happens before a multicast client exists:
Multicast
server
1.0.11
1.0.16
pe
r1
r2
ier
pe
oo
oo
er
Blocked
by STP
Multicast
Pontential
client
Sn
Sn
Qu
1. Querier starts receiving multicast stream
from server. Querier has no interested
clients so doesn’t forward multicast.
1.0.3
GQ
1.0.11
1.0.16
Sn
r1
ier
pe
er
oo
Qu
2. Querier sends General Query (GQ)
to find out if any would-be clients exist.
Snooper 1 receives Query on port 1.0.16,
snoops Query, and creates All Groups
entry for port 1.0.16.
1.0.3
Multicast
1.0.11
1.0.16
oo
r1
ier
pe
er
GQ
Sn
Qu
3. Snooper 1 forwards Query out all ports.
No clients exist, so no clients reply to
Query.
GQ
1.0.3
Multicast
Client
1.0.11
Sn
r1
ier
pe
er
oo
Qu
4. Client joins group by sending Membership
Report to the group address.
1.0.16
Report
1.0.3
Multicast
Report
1.0.16
Sn
r1
ier
pe
er
oo
Qu
5. Snooper 1 receives Report on port 1.0.3,
snoops Report, and adds a group entry
for port 1.0.3. Snooper 1 forwards Report
out its All Groups port.
1.0.11
1.0.3
Multicast
Multicast
6. Querier receives Report on port 1.0.11
and adds a group entry for port 1.0.11.
Querier starts forwarding multicast
stream out port 1.0.11.
1.0.11
1.0.16
Sn
r1
ier
pe
er
oo
Qu
1.0.3
Multicast
Multicast
1.0.11
1.0.16
Sn
r1
ier
pe
er
oo
Qu
7. Snooper 1 receives multicast stream
and forwards it out port 1.0.3.
Multicast
1.0.3
Multicast
GQ
1.0.11
1.0.16
Sn
r1
ier
pe
er
oo
Qu
8. Querier continues to send
General Queries periodically.
These keep All Groups entries
alive on Snoopers.
Multicast
Multicast
1.0.3
Multicast
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 9
IGMP snooping
Configuration Example
This example has a three-switch loop, as shown in the following figure. Switch-1 (x900) is
running IGMP and the other two switches (x600) are running IGMP snooping.
In AlliedWare Plus, both IGMP snooping and RSTP are enabled by default. On the x900 and
x600s, the only configuration needed is to set the client-facing ports as spanning tree edge
ports.
Multicast
Server
port1.0.1
00
x9
port1.0.11
Switch-1:
Querier
port1.0.12
Switch-2:
Snooper
port1.0.11
Switch-3:
Snooper
port1.0.12
port1.0.11
00
x6
00
x6
port1.0.12
(blocked by STP)
port1.0.1
Clie
nt
1
port1.0.1
Clie
nt
2
1. Configure Switch-1 (x900)
Switch-1 is configured with IGMP, which makes it the IGMP Querier in this network. It is best
practice to make the Querier the closest switch to the multicast source, and in this example
Switch-1 is closest. For more information about Queriers see "Multiple potential IGMP
Queriers" on page 16.
In this example, we add an IP interface to vlan100 and enable IP IGMP on this interface so that
Switch-1 becomes the IGMP Querier in this network.
Page 10 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP snooping
The default version of IGMP in AlliedWare Plus is IGMPv3. In this example we change it to
IGMPv2 to match the version the clients are using.
!
hostname Switch-1
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
!
interface vlan100
ip address 192.168.100.254/24
ip igmp
ip igmp version 2
AlliedWare Plus provides two ways of making this switch the Querier: as above, or by entering
the following commands:
awplus# conf t
awplus(config)# int vlan100
awplus(config-if)# ip igmp snooping querier
These commands enable IGMP Querier operation on a VLAN when no multicast routing
protocol is configured in the VLAN. When enabled, the IGMP Snooping Querier sends out
periodic IGMP queries for all interfaces on that VLAN. This command applies to interfaces
configured for IGMP Snooping.
This Snooping Querier function is a useful way to provide a Querier in an Layer 2 network that
does not contain a multicast router. We do not recommend enabling the IGMP Snooping
Querier feature on a Layer 2 switch when there is a router acting as an operational IGMP
Querier in the network.
In terms of IGMP querying activity, there is no real difference between the Querier and
Snooping Querier, they both send queries on the specified interface.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 11
IGMP snooping
2. Configure Switch-2 (x600)
Switch-2 is an IGMP Snooper. It forwards multicast packets and IGMP messages as required.
IGMP snooping is enabled by default and does not need any configuration.
!
hostname Switch-2
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
3. Configure Switch-3 (x600)
Switch-3 is also an IGMP Snooper. It forwards multicast packets and IGMP messages as required.
IGMP snooping is enabled by default and does not need any configuration.
!
hostname Switch-3
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
Page 12 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP snooping
Using the show command output to investigate IGMP state
No group members
At first we have no hosts requesting any multicast. The multicast server is streaming group
224.12.13.14 to the Querier, Switch-1. Switch-1 knows about the group, but has nobody
interested in receiving it. You can see this by using the command show ip igmp snooping
statistics interface vlan100 on Switch-1. The output of this command shows that Switch-1 has
an entry for the group, but no associated ports.
Switch-1#sh ip igmp snooping statistics int vlan100
IGMP Snooping statistics for vlan100
Group Type:
UnReg MC Group
Interface:
vlan100
Group:
224.12.13.14
Uptime:
00:00:10
Group mode:
Include (Expires: 00:04:10)
Last reporter: 192.168.100.100
No ports are mentioned in the output. Also, you can see that the Group Type is described as
"unReg MC Group". This means that it is an entry for an unregistered group. That is a group for
which data packets are arriving, but no IGMP reports have been received.
Client joins the group
When a client joins the group, the Group List changes for the Snooper that the client is attached
to, and on the Querier. First, look at the output of the command show igmp snooping statistics
interface vlan100 on the Snooper.
Switch-2#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Group Type:
Router Port Learnt
Interface:
vlan100
Group:
224.0.0.2
Uptime:
00:29:24
Group mode:
Include ()
Last reporter: 192.168.100.254
Port member list:
port1.0.11 - 169 secs
Interface:
vlan100
Group:
224.12.13.14
Flags:
Uptime:
00:00:30
Group mode:
Exclude (Expires: 00:03:50)
Last reporter: 192.168.100.10
Source list is empty
Port member list:
port1.0.1 - 230 secs
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 13
IGMP snooping
This output now shows two entries, one for each of the following:

Group 224.12.13.14 and port 1.0.1. This shows that the client is attached to the Snooper
through port 1.0.1 and is listening to group 224.12.13.14. The Snooper created this entry at
stage 5 in the process ("Explanation of IGMP Snooping" on page 9). This entry means that
the Snooper forwards packets from 224.12.13.14 out port 1.0.1.

Group Type: Router port learnt on port 1.0.11. This shows that the Snooper is connected to
the Querier through port 1.0.11. The Snooper created this entry at stage 2 in the process.
This entry means that the Snooper forwards IGMP reports and Leave messages out port
1.0.11. The Router Port entry means that the Snooper forwards the report from the client
out port 1.0.11 to the Querier, Switch-1.
Let us take the opportunity here to examine the information that appears in the output of the
show ip igmp snooping statistics interface command.

Group Type—This item only appears in entries that are Router Port or Unregistered group
entries. For standard entries created for IGMP reports, this item does not appear.

Interface—The interface which the IGMP reports were received on. In the case of a Router
Port entry, the VLAN towards the router. For unregistered groups it is the VLAN the stream
is arriving on.

Group—The multicast group address

Uptime—How long the entry has been in existence

Group mode—This parameter can either be Include or Exclude. The terms "Include" and
"Exclude" come from IGMPv3 terminology. IGMPv3 has the concept of including sources or
excluding sources that the group can be received from. If a group entry is created by IGMPv2
reports, then the entry will be labelled as "Exclude", because IGMPv2 reports are treated as
being “Exclude no source” reports. A Router Port entry is labelled as "Include" as this entry
effectively includes no sources.

Last reporter—The IP address of the last member to send an IGMP report for this group. In
the case of a router port, it is the address of the router or Querier that the router-indicating
packets are coming from. In the case of an unregistered group, it is the source address of the
stream.
The Querier receives the Report on port 1.0.11. Next, look at the output of the command
show ip igmp groups on the Querier.
Switch-1# sh ip igmp int vlan100
Interface vlan100 (Index 400)
IGMP Enabled, Active, Querier, Configured for version 2
Internet address is 192.168.100.254
Page 14 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP snooping
Switch-1# sh ip igmp groups
IGMP Connected Group Membership
Group Address
Interface
224.12.13.14
vlan100
Uptime
Expires
00:08:17 00:03:31
Last Reporter
0.0.0.0
The output above shows an entry for group 224.12.13.14. This entry shows that the Querier
knows about a client for 224.12.13.14. The Querier created this entry at stage 6 in the process.
The fact that the "Last Reporter" in this entry is 0.0.0.0 indicates that the report that created this
entry was not received from a directly connected host (the report was received via Switch-2).
Because the report was forwarded by a snooper that has no IP address, the report arrived with
IP source address 0.0.0.0.
Finally, look at the output of the command show ip igmp snooping statistics interface vlan100
on the Querier. Even though Switch-1 is the Querier for this network instead of a Snooper, this
command shows that a client for group 224.12.13.14 is reached out port 1.0.11. So a Querier
does also perform snooping, to work out the exact egress port(s) for each group.
Switch-1# sh ip igmp snooping statistics int vlan100
IGMP Snooping statistics for vlan100
Interface:
vlan100
Group:
224.12.13.14
Uptime:
00:12:11
Group mode:
Exclude (Expires: 00:03:43)
Last reporter: 0.0.0.0
Source list is empty
Port member list:
port1.0.11 - 224 secs
When a client leaves a group
When a client wants to stop receiving a group’s multicast stream, it sends an IGMP leave
message with a destination address of the group. The Snooper forwards the Leave message out
its All Groups port, so the message arrives at the IGMP Querier. At this point, the IGMP
Querier sends a series of Specific Queries (two by default) to see if anybody else is still listening
to this group.
If the Snooper receives a response to the Specific Queries, it forwards the response to the
Querier and continues to forward the multicast stream to the ports that want to receive it. If the
Snooper does not receive a response to the Specific Queries, it stops forwarding the stream.
For a detailed description of how the leave process works, see "How clients leave groups:
queries and timers" on page 59.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 15
Multiple potential IGMP Queriers
Multiple potential IGMP Queriers
To find out more about IGMP, we next investigate what happens when more than one router
has an IGMP configuration.
RFC 2236, Internet Group Management Protocol, Version 2, states that each Layer 2 network
should have only one IGMP Querier. You may configure IGMP on more than one router,
perhaps for redundancy, but the routers have a pseudo-election and the device with the lower
IP becomes the operating IGMP Querier.
This is a ‘pseudo-election; in reality, it is a query suppression, in that all queriers except that with
the lowest IP address just stop sending out queries when they realise that the network contains
a querier with a lower IP address than themselves. Each querier will send out regular queries.
When a querier receives a query message with a lower IP address then it will stop sending its
own queries for the duration of the Other Querier interval. As long as the other querier keeps
regularly sending queries, the higher IP address querier will not send queries. A snooping querier
(with source address of 0.0.0.0) should consider all real IP addresses to be ‘lower’ and stop
sending queries when it receives queries from a non-snooping querier.
The following example describes a network with two potential Queriers.
Page 16 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Multiple potential IGMP Queriers
Example
The network for this example uses the same loop as for "IGMP snooping" on page 8 and is
shown in the following figure.
Multicast
Server
port1.0.1
00
x9
port1.0.11
Switch-1:
Potential Querier
port1.0.12
Switch-2:
Elected Querier
port1.0.11
Switch-3:
Snooper
port1.0.12
port1.0.11
00
x6
00
x6
port1.0.12
(blocked by STP)
port1.0.1
Clie
nt
1
port1.0.1
Clie
nt
2
Both Switch-1 and Switch-2 are configured with IGMP, making both of them potential Queriers.
Switch-3, by default configuration, is an IGMP Snooper.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 17
Multiple potential IGMP Queriers
1. Configure Switch-1
Switch-1 is a potential IGMP Querier. It acts as a Snooper if it is not elected as the Querier
!
hostname Switch-1
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
!
interface vlan100
ip address 192.168.100.254/24
ip igmp
ip igmp version 2
Page 18 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Multiple potential IGMP Queriers
2. Configure Switch-2
Switch-2 is also a potential IGMP Querier. It acts as a Snooper if not elected as the Querier.
!
hostname Switch-2
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
!
interface vlan100
ip address 192.168.100.253/24
ip igmp
ip igmp version 2
3. Configure Switch-3
Switch-3 is an IGMP Snooper. It forwards multicast packets and IGMP messages as required.
IGMP snooping and Rapid Spanning Tree Protocol are enabled by default, so it does not need
any specific IGMP or RSTP configuration. (The configuration is the same as the configuration
used in the first example).
!
hostname Switch-3
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 19
Multiple potential IGMP Queriers
Explanation of Multiple Potential IGMP Queriers
When there are no group members
Switch-1 and Switch-2 are both possible Queriers, and an election determines which switch
becomes the actual Querier. We can see the results of the election by using the command
show ip igmp on each switch.
When there are two or more possible Queriers on the same network, the election process is
based on the lowest IP address. So in this example Switch-2, which has the IP address of
192.168.100.253, will be the Designated Querier as it has the lowest IP address.
On Switch-1, we see that it reports itself as the non-querier, and shows that the Querier is
192.168.100.253, which is Switch-2.
Switch-1# sh ip igmp int vlan100
Interface vlan100 (Index 400)
IGMP Enabled, Active, Non-Querier, Configured for version 2
Internet address is 192.168.100.254
IGMP interface has 3 group-record states
IGMP activity: 93 joins, 0 leaves
IGMP querying router is 192.168.100.253
IGMP robustness variable is 2
IGMP last member query count is 2
IGMP query interval is 125 seconds
IGMP Startup query interval is 31 seconds
IGMP Startup query count is 2
IGMP query holdtime is 500 milliseconds
IGMP querier timeout is 255 seconds
IGMP max query response time is 10 seconds
Last member query response interval is 1000 milliseconds
Group Membership interval is 260 seconds
IGMP Last member query count is 2
Strict IGMPv3 ToS checking is disabled on this interface
Source Address checking is enabled
IGMP Snooping is globally enabled
IGMP Snooping query solicitation is globally enabled for Root/Master
Nodes
IGMP Snooping query solicitation is globally disabled for Non Root/
Master Nodes
Num. query-solicit packets: 0 sent, 0 recvd
IGMP Snooping is enabled on this interface
IGMP Snooping fast-leave is not enabled
IGMP Snooping querier is not enabled
IGMP Snooping report suppression is enabled
Now we look at Switch-2, which has the lower IP address configured, resulting in it being the
Designated Querier based on the IGMP Querier election process.
Page 20 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Multiple potential IGMP Queriers
Switch-2#sh ip igmp int vlan100
Interface vlan100 (Index 400)
IGMP Enabled, Active, Querier, Configured for version 2
Internet address is 192.168.100.253
IGMP interface has 3 group-record states
IGMP activity: 18 joins, 1 leaves
IGMP robustness variable is 2
IGMP last member query count is 2
IGMP query interval is 125 seconds
IGMP Startup query interval is 31 seconds
IGMP Startup query count is 2
IGMP query holdtime is 500 milliseconds
IGMP querier timeout is 255 seconds
IGMP max query response time is 10 seconds
Group Membership interval is 260 seconds
IGMP Last member query count is 2
Last member query response interval is 1000 milliseconds
Strict IGMPv3 ToS checking is disabled on this interface
Source Address checking is enabled
IGMP Snooping is globally enabled
IGMP Snooping query solicitation is globally enabled for Root/Master
Nodes
IGMP Snooping query solicitation is globally disabled for Non Root/
Master Nodes
Num. query-solicit packets: 0 sent, 0 recvd
IGMP Snooping is enabled on this interface
IGMP Snooping fast-leave is not enabled
IGMP Snooping querier is not enabled
IGMP Snooping report suppression is enabled
The highlighted text shows that this switch has become the Designated Querier for vlan100.
The Source now sends a stream onto the LAN. With no clients requesting the stream, we look
at the IGMP Snooping statistics on Switch-1. We can see that the router port has been learnt
from the IGMP Querier (Switch-2). There are no ports associated with the multicast group
224.12.13.14 as no users have requested this group. Again, this appears with Group Type of
“UnReg MC Group”
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 21
Multiple potential IGMP Queriers
Switch-1#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Group Type:
Router Port Learnt
Interface:
vlan100
Group:
224.0.0.2
Uptime:
00:24:44
Group mode:
Include ()
Last reporter: 192.168.100.253
Port member list:
port1.0.11 - 168 secs
Group Type:
Interface:
Group:
Uptime:
Group mode:
Last reporter:
UnReg MC Group
vlan100
224.12.13.14
00:00:13
Include (Expires: 00:04:07)
192.168.100.100
From Switch-2, the IGMP Querier, we can see from the output that it is receiving this group, but
there are no interfaces associated with this, as no clients have requested that stream. So it
appears as an UnReg MC Group.
Switch-2#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Interface:
vlan100
Group Type:
UnReg MC Group
Interface:
vlan100
Group:
224.12.13.14
Uptime:
00:03:58
Group mode:
Include (Expires: 00:00:21)
Last reporter: 192.168.100.100
The reason that the stream arrives at Switch-2 is because Switch-1 will forward all multicast out
its Router Port.
When a client joins a group
Now imagine that Client 2 sends a Membership Report to Switch-3 for the group 224.12.13.14.
If we check the group membership for Switch-2 by using the command show ip igmp snooping
statistics interface vlan100, we see a group entry for 224.12.13.14. It has changed from being an
UnReg MC group entry to a normal forwarding entry.
We can see that this membership report from the client (192.168.100.20/24), which is attached
to port1.0.1 on Switch-3, has been received on port1.0.11 on Switch-2.
In this case, we see that the "Last reporter" in the entry on Switch-2 is 192.168.100.254. This is
because the report was forwarded to Switch-2 via Switch-1. Given that Switch-1 has the IP
address 192.168.100.254 on vlan100, it put that IP address as the source address of the IGMP
report when it forwarded it.
Page 22 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Multiple potential IGMP Queriers
Switch-2#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Interface:
vlan100
Group:
224.12.13.14
Flags:
Uptime:
00:01:49
Group mode:
Exclude (Expires: 00:03:08)
Last reporter: 192.168.100.254
Source list is empty
Port member list:
port1.0.11 - 189 secs
On Switch-3, we can see that reports have been received from a client (192.168.100.20) which
is attached to port 1.0.1:
Switch-3#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Group Type:
Router Port Learnt
Interface:
vlan100
Group:
224.0.0.2
Uptime:
00:13:02
Group mode:
Include ()
Last reporter: 192.168.100.253
Port member list:
port1.0.12 - 204 secs
Interface:
vlan100
Group:
224.12.13.14
Flags:
Uptime:
00:03:19
Group mode:
Exclude (Expires: 00:03:24)
Last reporter: 192.168.100.20
Source list is empty
Port member list:
port1.0.1 - 204 secs
If we check the group membership for Switch-1 and Switch-3, we see there are entries for
224.12.13.14, but also see a Router Port entry on each switch. The Router Port entry points to
the Querier, Switch-2. The output for Switch-1, for example, shows port 1.0.11 as the Router
port, indicating that Switch-1 reaches the Querier via port 1.0.11.
Switch-1 has received the Membership report on port1.0.12 (this is the connection to Switch3).
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 23
IGMP proxy
Switch-1#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Group Type:
Router Port Learnt
Interface:
vlan100
Group:
224.0.0.2
Uptime:
00:41:56
Group mode:
Include ()
Last reporter: 192.168.100.253
Port member list:
port1.0.11 - 136 secs
Interface:
vlan100
Group:
224.12.13.14
Uptime:
00:06:51
Group mode:
Exclude (Expires: 00:02:18)
Last reporter: 0.0.0.0
Source list is empty
Port member list:
port1.0.12 - 139 secs
We see port1.0.12 on Switch-1 port member list because interface port1.0.11 on Switch-3 is in
a RSTP Discarding state (this is the connection to Switch-2.) The traffic is going to be received
on interface port1.0.12 on Switch-1.
IGMP proxy
In very simple tree-design networks, IGMP Proxy is a useful simple alternative to a multicast
routing protocol for multicasting between VLANs.
An IGMP Proxy sends IGMP Membership Report and Leave group messages to an upstream
subnetwork on behalf of downstream devices, and sends Queries downstream. In other words,
an IGMP Proxy effectively ferries IGMP messages from one VLAN to another. The IGMP Proxy
looks like an IGMP Querier to the downstream VLAN, and like a client to the upstream VLAN.
Note that the Proxy can only have one configured upstream VLAN.
The IGMP packets forward at line speed, and the switch creates hardware entries as it receives
the IGMP requests and multicast data. This means that they are not sent to the CPU for
processing.
Page 24 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP proxy
Example
IGMP Proxy only works in tree networks, so for this example we convert the network from a
loop into a tree by disabling port 1.0.11 on Switch-1 (x900 switch). Switch-3 is the IGMP Proxy.
Switch-1 is upstream of the Proxy. Switch-2 is downstream of the Proxy on vlan100. Therefore,
the multicast server and Client 1 are now in different VLANs and Switch-3 sits on the boundary
between the two VLANs. This network is shown in the following figure.
00
x9
port1.0.1
vlan200
Multicast
Server
Switch-1:
Querier
port1.0.12
upsteam
vlan200
port1.0.12
port1.0.1
port1.0.11
downsteam
vlan100
00
x6
00
x6
Switch-2:
Snooper
port1.0.12
Switch-3:
Proxy
Clie
nt
1
1. Configure Switch-1.
Switch-1, the closest switch to the multicast source, is an IGMP Querier.
On Switch-1, we have shut down port1.0.11, which is the connection to Switch-2.
Switch-1(config)# int port1.0.11
Switch-1(config-if)# shutdown
The VLAN has also been changed from vlan100 to vlan200 and we have configured a static
route to the vlan100 subnet. So now the configuration for Switch-1 looks as follows:
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 25
IGMP proxy
!
hostname Switch-1
!
vlan database
vlan 200 name vlan200
!
interface port1.0.1-1.0.10
switchport access vlan 200
!
interface port1.0.11
shutdown
switchport access vlan 200
!
interface port1.0.12-1.0.24
switchport access vlan 200
!
interface vlan200
ip address 192.168.200.253/24
ip igmp
ip igmp version 2
!
ip route 192.168.100.0/24 192.168.200.254
2. Configure Switch-2.
Switch-2 is an IGMP Snooper. IGMP snooping is enabled by default and does not need any
configuration. We have added an IP route to the source's subnet 192.168.200.0/24.
!
hostname Switch-2
!
vlan database
vlan 100 name vlan100
vlan 100 state enable
!
interface port1.0.1-1.0.24
switchport access vlan 100
!
interface vlan100
ip address 192.168.100.252/24
!
ip route 192.168.200.0/24 192.168.100.253
Page 26 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP proxy
3. Configure Switch-3.
Switch-3 is an IGMP Proxy.
hostname Switch-3
!
ip multicast-routing
!
vlan database
vlan 100 name vlan100
vlan 200 name vlan200
!
interface port1.0.1-1.0.23
switchport access vlan 100
!
interface port1.0.24
switchport access vlan 200
!
!
interface vlan100
ip address 192.168.100.254/24
ip igmp
ip igmp mroute-proxy vlan200
ip igmp version 2
!
interface vlan200
ip address 192.168.200.254/24
ip igmp
ip igmp proxy-service
ip igmp version 2
Switch-3 has had the most configuration changes in this setup. The upstream interface is
vlan200, as this interface is closest to the multicast source, connected to Switch-1. The
downstream interface is vlan100, which has the clients requesting the stream 224.12.13.14. Since
we are now routing the multicast group 224.12.13.14 from vlan200 to vlan100, we have enabled
IP multicast-routing on Switch-3:
Switch-3(config)# ip multicast-routing
Let us now look in a bit more detail at the meaning of the IGMP Proxy commands. (Explanations
below.)
Switch-3(config)# int vlan200
Switch-3(config-if)# ip igmp proxy-service
On vlan200, we have enabled the IGMP proxy service. What this means is that all associated
downstream IGMP mroute proxy interfaces will have their IGMP packets forwarded directly to
this interface. The proxy will then transmit these packets towards the server attached to this
interface.
Switch-3(config)# int vlan100
Switch-3(config-if)# ip igmp mroute-proxy vlan200
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 27
IGMP proxy
This downstream mroute proxy interface listens for IGMP Report and Leave messages, and
forwards them to the upstream IGMP proxy service interface.
Note:
IGMP proxy does not work with other multicast routing protocols, such as PIM-SM or
PIM-DM.
Explanation of IGMP Proxy
When there are no group members
The multicast server streams group 224.12.13.14 to Switch-1 through port 1.0.1. IGMP
snooping detects the stream, as you can see by using the command show ip igmp snooping
statistics interface vlan200 on Switch-1.
Switch-1#sh ip igmp snooping statistics interface vlan200
IGMP Snooping statistics for vlan200
Group Type:
UnReg MC Group
Interface:
vlan200
Group:
224.12.13.14
Uptime:
00:00:02
Group mode:
Include (Expires: 00:04:17)
Last reporter: 192.168.200.100
When a client joins a group
Client 1 (attached to Switch-2, the Snooper) sends an IGMP Membership Report for the group
224.12.13.14. Switch-2 forwards that report message out its Router port, in this case port
1.0.12.
Switch-2#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Group Type:
Router Port Learnt
Interface:
vlan100
Group:
224.0.0.2
Uptime:
00:00:59
Group mode:
Include ()
Last reporter: 192.168.100.253
Port member list:
port1.0.12 - 201 secs
Interface:
vlan100
Group:
224.12.13.14
Flags:
Uptime:
00:00:54
Group mode:
Exclude (Expires: 00:03:26)
Last reporter: 192.168.100.10
Source list is empty
Port member list:
port1.0.1 - 206 secs
Page 28 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP proxy
Switch-3—the Proxy—receives the report on its downstream interface, vlan100. Switch-3 then
creates a new report with itself as the sender. It sends this report upstream to Switch-1 through
vlan200. Output of the commands show ip igmp groups and show ip igmp snooping interface
vlan100 show that Switch-3 knows of a client interested in the group 224.12.13.14 through port
1.0.11 on vlan100.
Switch-3#sh ip igmp groups
IGMP Connected Group Membership
Group Address
Interface
224.12.13.14
vlan100
224.12.13.14
vlan200
Uptime
Expires Last Reporter
00:58:48 00:02:20 192.168.100.252
00:58:48 00:04:14 192.168.100.252
The group 224.12.13.14 has been registered on both VLANs.
Switch-3#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Interface:
vlan100
Group:
224.12.13.14
Flags:
Uptime:
00:02:40
Group mode:
Exclude (Expires: 00:04:09)
Last reporter: 192.168.100.252
Source list is empty
Port member list:
port1.0.11 - 0 secs
The downstream client is reached through port1.0.11 via Switch-2. The Last Reporter address is
192.168.100.252, which is the IP address of Switch-2, because Switch-2 applied its IP address to
the IGMP reports when it forwarded them.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 29
IGMP proxy
Switch-3#sh ip igmp snooping statistics interface vlan200
IGMP Snooping statistics for vlan200
Group Type:
Router Port Learnt
Interface:
vlan200
Group:
224.0.0.2
Uptime:
00:01:01
Group mode:
Include ()
Last reporter: 192.168.200.253
Port member list:
port1.0.12 - 199 secs
Interface:
vlan200
Group:
224.12.13.14
Flags:
Uptime:
00:03:02
Group mode:
Exclude (Expires: 00:01:28)
Last reporter: 192.168.100.252
Source list is empty
Port member list:
On vlan200, the IGMP packets are transmitted out port 1.0.12.
Switch-3#sh ip igmp proxy
group
IGMP Connected Proxy Group Membership
Group Address
Interface
Member state
224.12.13.14
vlan200
Delay
We can see that the group has been received on vlan200 on the IGMP proxy switch. 'Delay'
means that none of the group or source group query timers run for the specified group. The
output above does not indicate whether the proxy works or not, it just tells us which groups are
registered in the system.
Switch-3#sh ip igmp int vlan100
Interface vlan100 (Index 400)
IGMP Enabled, Active, Querier, Configured for version 2
IGMP mroute-proxy interface is vlan200
Internet address is 192.168.100.253
The output above shows that Switch-3 is the active Querier on vlan100 and also that vlan200 is
the mroute-proxy interface.
The output below shows that vlan200 has the proxy configured and, importantly, that this
interface is not the active Querier.
Page 30 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP proxy
Switch-3#sh ip igmp int vlan200
Interface vlan200 (Index 500)
IGMP Enabled, Active, Non-Querier, Configured for version 2 proxyservice
IGMP host version 2
Internet address is 192.168.200.253
IGMP interface has 28 group-record states
IGMP activity: 0 joins, 0 leaves
IGMP querying router is 192.168.200.254
Switch-1 receives the proxied report from Switch-3. Switch-1 notes that Switch-3 is interested
in the group 224.12.13.14 and sends the group multicast to Switch-3 on port 1.0.12. Output of
the command show ip igmp snooping statistics interface vlan200 shows the membership that
Switch-1 is aware of.
Switch-1#sh ip igmp snooping statistics interface vlan200
IGMP Snooping statistics for vlan200
Interface:
vlan200
Group:
224.12.13.14
Uptime:
00:22:31
Group mode:
Exclude (Expires: 00:02:48)
Last reporter: 192.168.200.254
Source list is empty
Port member list:
port1.0.12 - 168 secs
When a client leaves a group
When the client on Switch-2 wants to stop receiving the group’s multicast stream, it sends an
IGMP Leave message. The switches use the above process to transfer the message to Switch-1.
Note the following points about how IGMP Proxy deals with Leave messages:

The Proxy sends an IGMP Leave Group message via its upstream interface only when the last
interface on the Proxy leaves the group.

The Proxy does not respond to IGMP Join or Leave Group messages received via its upstream
interface, but only to those received via downstream interfaces.

The Proxy does respond to IGMP query messages received via its upstream interface.
When the Proxy—Switch-3 in this example—sends a Leave Group message upstream, the
upstream IGMP Querier—Switch-1—sends a membership query. Switch-3 takes that query and
proxies it to the downstream interface, vlan100, with its own IP address as the source
(192.168.100.253). This means any other interested clients on Switch-2 can declare their interest
in continuing to receive the multicast stream.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 31
IGMP proxy
Multiple Proxies
A significant feature of AlliedWare Plus is that it can support multiple IGMP proxies on the same
switch.
Example configuration of multiple IGMP proxies
vlan database
vlan 40 name vlan40
vlan 50 name vlan50
vlan 60 name vlan60
vlan 100 name vlan100
vlan 200 name vlan200
!
interface port1.0.1-1.0.2
switchport
switchport mode access
switchport access vlan 100
!
interface port1.0.3-1.0.4
switchport
switchport mode access
switchport access vlan 40
!
interface port1.0.5-1.0.6
switchport
switchport mode access
switchport access vlan 50
!
interface port1.0.7-1.0.8
switchport
switchport mode access
switchport access vlan 60
Page 32 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP proxy
Example configuration of multiple IGMP proxies (cont.)
!
interface port1.0.24
switchport access vlan 200
!
interface vlan40
ip address 192.168.40.254/24
ip igmp
ip igmp mroute-proxy vlan50
ip igmp version 2
!
interface vlan50
ip address 192.168.50.254/24
ip igmp
ip igmp proxy-service
ip igmp version 2
!
interface vlan60
ip address 192.168.60.254/24
ip igmp
ip igmp mroute-proxy vlan50
ip igmp version 2
!
interface vlan100
ip address 192.168.100.254/24
ip igmp
ip igmp mroute-proxy vlan200
ip igmp version 2
!
interface vlan200
ip address 192.168.200.254/24
ip igmp
ip igmp proxy-service
ip igmp version 2
The configuration above has the following interfaces setup as the Proxy Service:

vlan200

vlan50
and the following interfaces as the host side (mroute proxy):

vlan40

vlan60

vlan100
Interfaces vlan40 and vlan60 are proxying to vlan50. Quite separately from these, interface
vlan100 is proxying to vlan200.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 33
Query solicitation (rapid recovery from topology changes)
Query solicitation (rapid recovery from topology
changes)
Query Solicitation minimizes loss of multicast data after a topology change. It is a built-in feature
of AlliedWare Plus managed Layer 3 switches when running EPSR or spanning tree (STP, RSTP,
or MSTP) for loop protection.
Without Query Solicitation, when the underlying link layer topology changes, multicast data flow
can stop for up to several minutes, depending on which port goes down and how much of the
timeout period was left (see "Why convergence takes so long without Query Solicitation" on
page 35). Query Solicitation greatly reduces this disruption.
Query Solicitation operates without configuration in networks of Allied Telesis managed layer 3
switches running STP, RSTP, MSTP or EPSR. You may find it helpful to manually enable it in the
following other situations:

loop-free networks running IGMP (see "Speeding up IGMP convergence in a non-looped
topology" on page 41)

networks in which not all switches support Query Solicitation (see "Enabling Query
Solicitation on multiple switches in a looped topology" on page 41)
How Query Solicitation works
Query Solicitation monitors STP, RSTP, MSTP and EPSR messages for topology changes. When it
detects a change, it generates a special IGMP Leave message called a Query Solicit. The switch
floods the Query Solicit message to all ports in every VLAN that Query Solicitation is enabled
on. When the Querier receives the Query Solicit message, it sends out a General Query and
waits for clients to respond with Membership Reports. These Reports update the snooping
information throughout the network.
Query Solicit messages have a group address of 0.0.0.0.
Query Solicitation works by default (without you enabling it) on all VLANs on the root bridge in
an STP instance and on all data VLANs on the master node in an EPSR instance. By default, the
root bridge or master node always sends a Query Solicit message when any of the following
events occur:

an STP BPDU packet with the Topology Change (TC) flag arrives at the root bridge

an STP port on a switch goes from a Discarding to Forwarding state

the FDB gets flushed by EPSR
If necessary, you can make clients respond more quickly to the General Query by tuning the
IGMP timers, especially the "Max Query Response Interval" on page 76.
Page 34 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Query solicitation (rapid recovery from topology changes)
The following figure shows how Query Solicitation works when a port goes down.
Multicast
h4
h3
itc
itc
Sw
Sw
2
h
itc oot
Sw P r
ST
1
h
itc ier
Sw uer
Q
Initial state:
Port on Switch 3
is blocking.
Multicasts flow
from server to
client via Switches
1 and 4
Multicast
Multicast
h3
itc
Sw
2
h
itc oot
Sw P r
ST
1. Link to Switch 4
goes down.
Switch 3 stops
blocking and
sends topology
change (TC)
TC
2
h
itc oot
Sw P r
ST
2. Switch 2 receives
TC and sends
Query Solicit (QS)
QS
QS
GQ
GQ
GQ
GQ
Report
Report
Report
1
h
itc ier
Sw uer
Q
3. Switch 1 receives
QS and sends
General Query (GQ)
QS
4. Host receives GQ
and responds with
Membership Report
Report
Sw
Multicast
h4
h3
itc
itc
Multicast
Sw
Multicast
2
h
itc oot
Sw P r
ST
1
h
itc ier
Sw uer
Q
Final state:
Multicasts flow
from server to
client via Switches
1, 2, 3, and 4
Multicast
Multicast
Why convergence takes so long without Query Solicitation
This section illustrates IGMP convergence in a simple network that does not need STP because
it has no switch loops. In this case we have disabled STP on all switches. Query Solicitation is
disabled by default in networks like this, because no switch is an STP root bridge or an EPSR
master node.
In this network, it takes up to 125 seconds for multicasting to recover after a port comes back
up. This section explains the reason for the slow convergence. "Speeding up IGMP convergence
in a non-looped topology" on page 41 explains the solution.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 35
Query solicitation (rapid recovery from topology changes)
Example
The following figure shows the network for the example in this section.
Multicast
Server
Clie
nt
1
port1.0.9
port1.0.24
Switch-1:
Querier
port1.0.1
00
x6
00
x9
port1.0.1
Switch-2:
Snooper
The example considers what happens when a port comes up. When the port was down, the
client stopped receiving multicasts because there was no backup route available. The example
shows how the network recovers. The multicast group is 224.12.13.14.
1. Configure Switch-1.
Switch-1 is configured with IGMP, which makes it the IGMP Querier in this network.
!
hostname Switch-1
!
no spanning-tree rstp enable
!
interface vlan1
ip address 192.168.1.1/24
ip igmp
Page 36 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Query solicitation (rapid recovery from topology changes)
2. Configure Switch-2.
Switch-2 is an IGMP Snooper. It forwards multicast packets and IGMP messages as required.
IGMP snooping is enabled by default and does not need any configuration.
!
hostname Switch-2
!
!no spanning-tree rstp enable
!
interface vlan1
ip address 192.168.1.2/24
Explanation from the perspective of Switch-2, the Snooper
When link is
up
When the link is connected (all ports are up), the Snooper has entries for two ports:

port 1.0.9, which is the Snooper's connection to the client. The Snooper sends the multicast
stream out this port, as well as sending Queries (the Snooper floods Queries out all its ports)

port 1.0.1, which is the Snooper's connection to the Querier. This is a Router Port entry, so
the Snooper forwards Reports out this port. The output of the command show ip igmp
snooping statistics interface vlan1 shows both entries.
Switch-2#sh ip igmp snooping statistics interface vlan1
IGMP Snooping statistics for vlan1
Group Type:
Router Port Learnt
Interface:
vlan1
Group:
224.0.0.2
Uptime:
00:03:18
Group mode:
Include ()
Last reporter: 192.168.1.1
Port member list:
port1.0.1 - 218 secs
Interface:
vlan1
Group:
224.12.13.14
Flags:
Uptime:
00:01:49
Group mode:
Exclude (Expires: 00:03:41)
Last reporter: 192.168.1.10
Source list is empty
Port member list:
port1.0.9 - 221 secs
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 37
Query solicitation (rapid recovery from topology changes)
When link
goes down
When we disconnect port 1.0.1 on the Snooper, the Router Port disappears, and the entry for
224.12.13.14 is still present until it times out.
Switch-2#sh ip igmp snooping statistics interface vlan1
IGMP Snooping statistics for vlan1
Interface:
vlan1
Group:
224.12.13.14
Flags:
Uptime:
00:02:56
Group mode:
Exclude (Expires: 00:02:33)
Last reporter: 192.168.1.10
Source list is empty
Port member list:
port1.0.9 - 154 secs
Once the link is reconnected, we see that the Router Port has not been learnt.
Switch-2#sh ip igmp snooping statistics interface vlan1
IGMP Snooping statistics for vlan1
Interface:
vlan1
Group:
224.12.13.14
Flags:
Uptime:
00:05:01
Group mode:
Exclude (Expires: 00:00:28)
Last reporter: 192.168.1.10
Source list is empty
Port member list:
port1.0.9 - 29 secs
Eventually, the Querier sends an IGMP Query, which the Snooper receives on port 1.0.1. This
restores the All Groups port on the Snooper. By default the Querier sends General Queries
every 125 seconds, so the IGMP convergence delay will be up to 125 seconds with the default
settings. For more information about this timeout, see "Configurable IGMP timers and
counters" on page 68—but do not change the timeout without very carefully considering the
effect on your network.
When the Snooper receives the General Query, it forwards it out all its ports. The client
responds with a Report. The Snooper forwards the Report out its All Groups port towards the
Querier. The Querier responds by sending the multicast stream to the Snooper, which forwards
the multicast stream out port 1.0.9 to the client.
Page 38 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Query solicitation (rapid recovery from topology changes)
Switch-2#sh ip igmp snooping statistics interface vlan1
IGMP Snooping statistics for vlan1
Group Type:
Router Port Learnt
Interface:
vlan1
Group:
224.0.0.2
Uptime:
00:01:15
Group mode:
Include ()
Last reporter: 192.168.1.1
Port member list:
port1.0.1 - 216 secs
Interface:
vlan1
Group:
224.12.13.14
Flags:
Uptime:
00:06:32
Group mode:
Exclude (Expires: 00:03:36)
Last reporter: 192.168.1.10
Source list is empty
Port member list:
port1.0.9 - 217 secs
Explanation from the perspective of Switch-1, the Querier
When link is
up
When the link is connected (all ports are up), the Querier has an entry for port 1.0.1, so it
sends the group 224.12.13.14 out port 1.0.1. The output of the command show ip igmp
snooping statistics interface vlan1 shows this entry.
Switch-1#show ip igmp snooping statistics interface vlan1
IGMP Snooping statistics for vlan1
Interface:
vlan1
Group:
224.12.13.14
Uptime:
16:49:17
Group mode:
Exclude (Expires: 00:03:18)
Last reporter: 192.168.1.2
Source list is empty
Port member list:
port1.0.1 - 198 secs
When link
goes down
When we disconnect port 1.0.1 on the Snooper, the port disappears. The Querier is still
receiving the multicast stream from the server, so the group entry remains. We can see that the
group 224.12.13.14 is now an "UnReg MC Group".
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 39
Query solicitation (rapid recovery from topology changes)
Switch-1#sh ip igmp snooping statistics interface vlan1
IGMP Snooping statistics for vlan1
Group Type:
UnReg MC Group
Interface:
vlan1
Group:
224.12.13.14
Uptime:
00:00:05
Group mode:
Include (Expires: 00:04:15)
Last reporter: 192.168.1.5
When link
comes up
again
When we reconnect port 1.0.1 on the Snooper, the port does not reappear because the
Querier has not yet received a Report over it. Therefore, the Querier does not start forwarding
the multicast stream out the port at this time.
Eventually, the Querier sends an IGMP Query out all its ports. In response, it receives a Report
from the client (via the Snooper). This restores the port entry and the Querier starts sending
the multicast stream again.
The output of the commands show ip igmp snooping statistics interface vlan1 and show ip
igmp groups both show this restored entry.
Switch-1#sh ip igmp snooping statistics interface vlan1
IGMP Snooping statistics for vlan1
Interface:
vlan1
Group:
224.12.13.14
Uptime:
00:00:12
Group mode:
Exclude (Expires: 00:04:08)
Last reporter: 192.168.1.2
Source list is empty
Port member list:
port1.0.1 - 248 secs
Switch-1#sh ip igmp groups
IGMP Connected Group Membership
Group Address
Interface
224.12.13.14
vlan1
Uptime
Expires Last Reporter
00:00:21 00:03:59 192.168.1.2
Page 40 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Query solicitation (rapid recovery from topology changes)
Speeding up IGMP convergence in a non-looped topology
The previous section described how it can take up to 125 seconds for multicasting to recover in
a non-looped topology after a port comes back up. You can speed up convergence simply by
enabling RSTP. This enables the network to use Query Solicitation and means that multicasting
resumes within 3 seconds of the link coming up.
Even though there is no loop in the network, one of the switches becomes the STP root
bridge—it does not matter which switch does this. When the link comes up, the root bridge
detects the topology change and sends a Query Solicitation.
We disabled RSTP in the previous example. Even though RSTP is enabled by default in
AlliedWare Plus, we have to re-enable it for this example:
Switch-1# conf t
Switch-1(config)# spanning-tree rstp enable
Enabling Query Solicitation on multiple switches in a looped
topology
On networks that use spanning tree or EPSR, Query Solicitation is not normally required on
switches other than the STP root bridge or EPSR master node. Therefore, it is only enabled by
default on the root bridge and the master node.
However, in some networks you may need to turn on Query Solicitation on all switches—for
example, if the network includes other switches that do not support Query Solicitation and
therefore the STP root bridge may be a switch that does not send Query Solicit messages. To
enable Query Solicitation, use the commands:
awplus# configure terminal
awplus(config)# ip igmp snooping tcn query solicit
Every switch that has Query Solicitation enabled sends a Query Solicit message when it detects
a topology change. Enabling it on multiple switches means you get multiple messages, but has no
other disadvantage.
The following figure shows the packet flow for a four-switch network with Query Solicitation
enabled on all the switches.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 41
Query solicitation (rapid recovery from topology changes)
Multicast
itc
h3
Multicast
Multicast
h4
h3
itc
itc
Sw
Sw
QS from 3
QS from 3
GQ from 1
GQ from 1
GQ from 1
TC from 3
TC from 3
GQ from 1
h4
h3
itc
itc
Sw
Sw
2
h
itc oot
Sw P r
ST
1
h
itc ier
Sw uer
Q
2. Switch 2 receives TC
from switch 3.
Switch 2 sends QS.
to switch 1.
Switch 1 sends GQ
2
h
itc oot
Sw P r
ST
1
h
itc ier
Sw uer
Q
1. Link to switch 4
goes down.
Switch 3 stops
blocking and
sends Topology
Change (TC) and
Query Solicit (QS).
Switch 2 forwards
QS to switch 1.
Switch 1 sends
General Query (GQ)
QS from 2
GQ from 1
GQ from 1
GQ from 1
h4
h3
itc
itc
Sw
Sw
QS from 4
QS from 4
GQ from 1
GQ from 1
GQ from 1
GQ from 1
h4
h3
itc
itc
Sw
Sw
2
h
itc oot
Sw P r
ST
Report
Report
Report
Report
Report
Report
Report
Report
Report
Report
Report
Report
Sw
Multicast
h4
h3
itc
itc
Multicast
Sw
2
h
itc oot
Sw P r
ST
1
h
itc ier
Sw uer
Q
Multicast
GQ from 1
QS from 4
1
h
itc ier
Sw uer
Q
4. Client replies to each
GQ by sending
Membership Reports
2
h
itc oot
Sw P r
ST
1
h
itc ier
Sw uer
Q
3. Switch 4 receives TC
from switch 3.
Switch 4 sends QS.
towards switch 1.
Switch 1 sends GQ
Final state:
Multicasts flow
from server to
client via Switches
1, 2, 3, and 4
Sw
2
h
itc oot
Sw P r
ST
1
h
itc ier
Sw uer
Q
Initial state:
Port on switch 3
is blocking.
Multicasts flow
from server to
client via switches
1 and 4
Multicast
Multicast
One topology change caused three Query Solicits, three General Queries, and three Reports.
Page 42 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP filtering (controlling multicast distribution)
IGMP filtering (controlling multicast distribution)
IGMP filtering lets you control the distribution of multicast services on each switch port. Filtering
is useful for subscription services when clients must be explicitly authorised to view a multicast
stream.
Example
This example shows how to stop a host joining the group 224.0.1.22 and allow it to join all other
groups. It uses the same network configuration as "IGMP snooping" on page 8. For convenience,
the diagram is reproduced below.
Multicast
Server
port1.0.1
00
x9
port1.0.11
Switch-1:
Querier
port1.0.12
Switch-2:
Snooper
port1.0.11
Switch-3:
Snooper
port1.0.12
port1.0.11
00
x6
00
x6
port1.0.12
(blocked by STP)
port1.0.1
port1.0.1
Clie
nt
2
Clie
nt
1
The network contains a Windows 2000 workstation that regularly sends SVRLOC messages (an
IGMP Membership Report for 224.0.1.22). This group gets added to the list of groups in vlan100
on Switch-1, as shown in the following output of the show ip igmp command.
Switch-1>show ip igmp groups
IGMP Connected Group Membership
Group Address
Interface
224.0.1.22
vlan100
Uptime
Expires Last Reporter
00:03:27 00:03:04 0.0.0.0
We do not need to receive this multicast, so we will filter it out.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 43
IGMP filtering (controlling multicast distribution)
1. Configure Switch-1
Switch-1, the closest switch to the multicast source, is an IGMP Querier. AlliedWare Plus uses
access lists to accomplish the desired effect. Add an Access Control List (ACL) to a VLAN
interface configured for IGMP, IGMP Snooping or IGMP Proxy:
Switch-1(config)# ip igmp access-group
The access control list is used to control and filter the multicast groups learnt on the VLAN
interface.
To configure an ACL to block 224.0.1.22 and to attach the ACL to vlan100, use these
commands:
Switch-1#conf t
Switch-1(config)#access-list 1 deny 224.0.1.22 0.0.0.0
Switch-1(config)#int vlan100
Switch-1(config-if)#ip igmp access-group 1
Switch-1#show access-list 1
Standard IP access list 1
10 deny
224.0.1.22
Switch-1 configuration:
!
hostname Switch-1
!
access-list 1 deny 224.0.1.22
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
!
interface vlan100
ip address 192.168.100.254/24
ip igmp
ip igmp access-group 1
ip igmp version 2
Page 44 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP throttling (limiting the number of streams for each subscriber)
Switch-2 and Switch-3's configuration do not change from the first example ("Configuration
Example" on page 10).
We look at the command show ip igmp snooping statistics interface vlan100, and since
applying the filter, the stream 224.0.1.22 is no longer in the output:
Switch-1#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
IGMP throttling (limiting the number of streams for
each subscriber)
IGMP throttling allows you to limit the number of streams that subscribers may access at a given
time, for example, to protect from bandwidth oversubscription. When the number of multicast
group memberships associated with a switch port reaches the configured limit, the port can
either deny further Membership Reports, or replace an existing membership with the new
group.
IGMP filtering and throttling can be applied separately or together. The switch applies the filters
first, then subjects any multicast group memberships passed by the filter to the limits imposed by
throttling.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 45
IGMP throttling (limiting the number of streams for each subscriber)
Example
This example builds on "IGMP filtering (controlling multicast distribution)" on page 43 and uses
the same network configuration as "IGMP snooping" on page 8. For convenience, the diagram is
reproduced below.
Multicast
Server
port1.0.1
00
x9
port1.0.11
Switch-1:
Querier
port1.0.12
Switch-2:
Snooper
port1.0.11
Switch-3:
Snooper
port1.0.12
port1.0.11
00
x6
00
x6
port1.0.12
(blocked by STP)
port1.0.1
Clie
nt
1
Page 46 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
port1.0.1
Clie
nt
2
IGMP throttling (limiting the number of streams for each subscriber)
1. Configure Switch-1
Switch-1 is an IGMP Querier. It has the same filter configured as in the previous example, to
deny the multicast group 224.0.1.22.
!
hostname Switch-1
!
access-list 1 deny 224.0.1.22
!
spanning-tree mode rstp
!
vlan database
vlan 100 state enable
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
!
interface vlan100
ip address 192.168.100.254/24
ip igmp
ip igmp access-group 1
ip igmp version 2
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 47
IGMP throttling (limiting the number of streams for each subscriber)
2. Configure Switch-2
Switch-2 is an IGMP Snooper. IGMP snooping is enabled by default and does not need any
configuration. Switch-2 is limited to three multicast groups on vlan100. We have also added the
filter that was configured on Switch-1 to deny the multicast group 224.0.1.22.
!
hostname Switch-2
!
access-list 1 deny 224.1.0.22
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
!
interface vlan100
ip igmp access-group 1
ip igmp limit 3
Page 48 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP throttling (limiting the number of streams for each subscriber)
3. Configure Switch-3
Switch-3 is also an IGMP Snooper.
!
hostname Switch-3
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
Explanation of IGMP throttling
In this example, Switch-2's configuration limits vlan100 to three concurrent multicast groups.
Consider Switch-2 after a client on port 1.0.1 has tried to join the three groups from
224.12.13.14 - 224.12.13.16. Output from the command show ip igmp snooping statistics
interface vlan100 shows the two memberships.
Output from the show ip igmp snooping statistics interface vlan100 command
Switch-2#show ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Group Type:
Router Port Learnt
Interface:
vlan100
Group:
224.0.0.2
Uptime:
02:12:43
Group mode:
Include ()
Last reporter: 192.168.100.254
Port member list:
port1.0.11 - 172 secs
Interface:
Group:
Flags:
Uptime:
Group mode:
...
vlan100
224.12.13.14
00:51:03
Exclude (Expires: 00:02:54)
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 49
Static IGMP
Output from the show ip igmp snooping statistics interface vlan100 command (cont.)
...
Last reporter: 192.168.100.10
Source list is empty
Port member list:
port1.0.1 - 175 secs
Interface:
vlan100
Group:
224.12.13.15
Flags:
Uptime:
00:16:00
Group mode:
Exclude (Expires: 00:02:56)
Last reporter: 192.168.100.10
Source list is empty
Port member list:
port1.0.1 - 177 secs
Group Type:
Interface:
Group:
Uptime:
Group mode:
Last reporter:
UnReg MC Group
vlan100
239.255.255.253
00:05:14
Include (Expires: 00:01:26)
192.168.1.100
The switch has three entries in the IP IGMP snooping table, and even though the client attached
to Switch-2 was trying to access the streams 224.12.13.14, 224.12.13.15 and 224.12.13.16, it has
only joined streams 224.12.13.14 and 224.12.13.15, as Switch-2 has also got an entry for the
239.255.255.253 group (SLP multicast address). The limit of three has been reached, so
224.12.13.16 is not present in the table and the client cannot receive this group.
Static IGMP
Static IGMP enables you to configure a switch with specified group-to-interface or group-to-port
mappings, which you may want to do if:

your network includes hosts that cannot send IGMP Membership Reports

you need to guarantee that a specific multicast stream is instantly available on a port, without
any delay from the joining process
A common usage of Static IGMP is for protocols like Service Location Protocol (SLP). This
protocol sends out multicast packets that need to be forwarded to designated ports. You may
want SLP packets to be forwarded to ports that have servers who need to respond to these
packets. Static IGMP allows you to specify that traffic for this group should go to hosts who will
respond to, or are interested in, these messages.
Page 50 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Static IGMP
Example
In this example, we will start by setting an IGMP static entry for the group 224.12.13.14 to go to
port 1.0.5 on Switch-1 (part of vlan100). On that port, we have attached a host that has no
multicast client software running. After examining the effect of static IGMP on Switch-1, we will
add a static IGMP entry to Switch-3 and consider the effect this has on multicasting through the
network. The network for this example has three switches in a loop and is shown in the
following figure.
Sta
Clietic
nt
port1.0.5
00
x9
port1.0.1
Multicast
Server
port1.0.11
port1.0.11
Switch-1:
Querier
port1.0.12
Switch-3:
port1.0.12
00
x6
00
x6
port1.0.12
port1.0.11
(blocked by STP)
port1.0.5
Switch-2:
Snooper
Sta
Clietic
nt
(added later in example)
1. Configure Switch-1.
Switch-1 is an IGMP Querier and has the static IGMP entry. Static IGMP also requires you to:

add an IP address to the interface to which you will attach the static entry

enable IGMP

enable the interface as an IGMP interface
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 51
Static IGMP
The commands for adding a static entry to the switch are:
Switch-1# conf t
Switch-1(config)# int vlan100
Switch-1(config-if)# ip igmp static-group 224.12.13.14 int
port1.0.5
Configuration of Switch-1
!
hostname Switch-1
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
!
interface vlan100
ip address 192.168.100.254/24
ip igmp
ip igmp static-group 224.12.13.14 interface port1.0.5
ip igmp version 2
Page 52 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Static IGMP
2. Configure Switch-2.
Switch-2 is an IGMP Snooper.
!
hostname Switch-2
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
3. Configure Switch-3.
Switch-3 is also an IGMP Snooper.
!
hostname Switch-3
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.25-1.0.26
switchport
switchport mode access
!
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 53
Static IGMP
Explanation of Static IGMP
When the IGMP static entry is created on Switch-1, entries immediately appear in the IGMP
snooping table and the IGMP table.
Switch-1#show ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Interface:
vlan100
Group:
224.12.13.14
Uptime:
00:18:08
Group mode:
Exclude (Static)
Last reporter: 0.0.0.0
Source list is empty
Port member list:
port1.0.5 - 0 secs
Switch-1#sh ip igmp groups
IGMP Connected Group Membership
Group Address
Interface
224.12.13.14
vlan100
Uptime
00:19:01
Expires
stopped
Last Reporter
0.0.0.0
The reason that it states ‘stopped’ in the ‘Expires’ column is that it is a static entry, so this entry
will never time out. If there are no clients that have sent an IGMP Membership Report for the
static group then the 'Expires' entry shows 'stopped'. If the switch sees any IGMP Membership
Reports for the static group from clients, then the 'Expires' entry shows 'static'.
When the group 224.12.13.14 starts streaming into Switch-1, we can use the command show
interface port1.0.5 to watch the number of multicast packets sent on port1.0.5 increase. This
means that the link is up and the static IGMP entry is working.
Switch-1#show int port1.0.5
Interface port1.0.5
Scope: both
Link is UP, administrative state is UP
Thrash-limiting
Status Not Detected, Action learn-disable, Timeout 1(s)
Hardware is Ethernet, address is 0000.cd29.98ab
index 5005 metric 1 mru 1522
current duplex full, current speed 100, current polarity auto
configured duplex auto, configured speed auto, configured polarity auto
<UP,BROADCAST,RUNNING,MULTICAST>
SNMP link-status traps: Disabled
input packets 541, bytes 47972, dropped 0, multicast packets 147
output packets 2919, bytes 1031906, multicast packets 2259 broadcast packets 314
Time since last state change: 0 days 00:51:56
Page 54 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Static IGMP
Switch-1#show int port1.0.5
Interface port1.0.5
Scope: both
Link is UP, administrative state is UP
Thrash-limiting
Status Not Detected, Action learn-disable, Timeout 1(s)
Hardware is Ethernet, address is 0000.cd29.98ab
index 5005 metric 1 mru 1522
current duplex full, current speed 100, current polarity auto
configured duplex auto, configured speed auto, configured polarity auto
<UP,BROADCAST,RUNNING,MULTICAST>
SNMP link-status traps: Disabled
input packets 543, bytes 48284, dropped 0, multicast packets 149
output packets 3518, bytes 1842552, multicast packets 2858 broadcast packets 314
Time since last state change: 0 days 00:52:03
When we add a static entry on another switch
Now we add a static IGMP entry on port1.0.5 of Switch-3, by adding the configuration below.
!
interface vlan100
ip address 192.168.100.253/24
ip igmp
ip igmp static-group 224.12.13.14 interface port1.0.5
ip igmp version 2
Both switches are potential IGMP Queriers and Switch-3 becomes the Querier. This is because
we gave Switch-3 a lower IP address (192.168.100.253) than Switch-1 (192.168.100.254).
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 55
Static IGMP
To see the effect that the new configuration has on Switch-1, we can check the IGMP snooping
and IGMP tables. The IGMP snooping table shows that Switch-1 now has an All Groups entry
because it is no longer the Querier. The IGMP table also shows that Switch-1 is not the Querier.
Switch-1#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Group Type:
Router Port Learnt
Interface:
vlan100
Group:
224.0.0.2
Uptime:
00:46:58
Group mode:
Include ()
Last reporter: 192.168.100.253
Port member list:
port1.0.12 - 228 secs
Interface:
vlan100
Group:
224.12.13.14
Uptime:
00:57:06
Group mode:
Exclude (Static)
Last reporter: 0.0.0.0
Source list is empty
Port member list:
port1.0.5 - 0 secs
Switch-1#sh ip igmp groups
IGMP Connected Group Membership
Group Address
Interface
224.12.13.14
vlan100
Uptime
00:57:56
Expires
stopped
Last Reporter
0.0.0.0
We can see the static entry on Switch-3 by checking the IGMP snooping and IGMP tables.
Switch-3#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Interface:
vlan100
Group:
224.12.13.14
Flags:
SG
Uptime:
00:50:04
Group mode:
Exclude (Expires: 00:02:42, Static)
Last reporter: 192.168.100.254
Source list is empty
Port member list:
port1.0.5 - 0 secs
Page 56 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Static IGMP
Switch-3#sh ip igmp groups
IGMP Connected Group Membership
Group Address
Interface
224.12.13.14
vlan100
Uptime
Expires Last Reporter
00:52:16
static 192.168.100.254
The server connected to port1.0.1 on Switch-1 is transmitting group 224.12.13.14, so we can
see from the first output that Switch-3 has received the group 224.12.13.14 on port 1.0.12 and
the static entry is on port 1.0.5.
If the multicast server was attached to Switch-3 instead of Switch-1, we would have to change
Switch-3's configuration. We would need to add a static entry for the port that Switch-3 uses to
connect to Switch-1 (port 1.0.12). Although this is unnecessary in this scenario, we will do it to
demonstrate the effect, by using the following command:
awplus(config-if)# ip igmp static-group 224.12.13.14 interface
port1.0.12
To see the new static entry, we use the commands show ip igmp snooping statistics interface
vlan100 and show ip igmp group; to see multicast packets streaming, we use the command
show int port1.0.5 and show int port1.0.12 to view the counters.
Switch-3#sh ip igmp groups
IGMP Connected Group Membership
Group Address
Interface
224.12.13.14
vlan100
Uptime
Expires Last Reporter
01:12:18
static 192.168.100.254
Switch-3#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Interface:
vlan100
Group:
224.12.13.14
Flags:
SG
Uptime:
01:12:41
Group mode:
Exclude (Expires: 00:03:23, Static)
Last reporter: 192.168.100.254
Source list is empty
Port member list:
port1.0.5 - 0 secs
port1.0.12 - 0 secs
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 57
Static IGMP
Switch-3#sh int port1.0.5
Interface port1.0.5
Scope: both
Link is UP, administrative state is UP
Thrash-limiting
Status Not Detected, Action learn-disable, Timeout 1(s)
Hardware is Ethernet, address is 0015.77c2.4d55
index 5005 metric 1 mru 1500
current duplex full, current speed 100, current polarity mdix
configured duplex auto, configured speed auto, configured polarity
auto
<UP,BROADCAST,RUNNING,MULTICAST>
SNMP link-status traps: Disabled
input packets 19, bytes 1885, dropped 0, multicast packets 8
output packets 523, bytes 37273, multicast packets 417 broadcast
packets 106
Time since last state change: 0 days 00:13:29
Switch-3#sh int port1.0.12
Interface port1.0.12
Scope: both
Link is UP, administrative state is UP
Thrash-limiting
Status Not Detected, Action learn-disable, Timeout 1(s)
Hardware is Ethernet, address is 0015.77c2.4d55
index 5012 metric 1 mru 1500
current duplex full, current speed 1000, current polarity mdi
configured duplex auto, configured speed auto, configured polarity
auto
<UP,BROADCAST,RUNNING,MULTICAST>
SNMP link-status traps: Disabled
input packets 58783, bytes 10599594, dropped 0, multicast packets
50137
output packets 1725, bytes 197790, multicast packets 713 broadcast
packets 1 012
Time since last state change: 1 days 00:05:40
We can see that the counters have incremented on both ports.
Page 58 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
How clients leave groups: queries and timers
When a static entry's port goes down
Finally, note that when the port attached to a static entry goes down, the static entry remains.
You can see from the output of the command show ip igmp snooping statistics interface
vlan100 that port 5 has been disconnected.
Switch-1#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Group Type:
Router Port Learnt
Interface:
vlan100
Group:
224.0.0.2
Uptime:
01:35:25
Group mode:
Include ()
Last reporter: 192.168.100.253
Port member list:
port1.0.12 - 227 secs
Interface:
vlan100
Group:
224.12.13.14
Uptime:
01:45:33
Group mode:
Exclude (Static)
Last reporter: 0.0.0.0
Source list is empty
Port member list:
port1.0.5 - 0 secs
How clients leave groups: queries and timers
When a client leaves a group, the Snoopers and the Querier check which ports now have
clients that belong to that group. They will stop forwarding the group’s traffic out any ports that
are now unnecessary. In this section, we describe the process in detail.
Overview of leave process
The basic process when a client leaves a group is as follows:
1. The client sends a Leave message to indicate that it no longer needs to receive that multicast
group.
2. The Snooper receives the Leave message and forwards it towards the Querier.
3. For all ports that belong to the group, the Querier changes its internal group membership
timer to a short value (2 seconds by default—see Querier timer values below).
4. The Querier sends a Specific Query to ask which other clients still belong to that group.
5. The aforementioned Snooper receives the Specific Query. For all ports that belong to the
group, the Snooper changes its internal group membership timer to a short value (2 seconds
by default—see Snooper timer values below) unless the timer is already short. It forwards
the Query out all its ports.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 59
How clients leave groups: queries and timers
6. The Querier waits for the Last Member Query Interval time, 1 second by default, and then
sends a second Specific Query.
7. The aforementioned Snooper snoops this second Specific Query and uses it to set the
internal group membership timer for each port, unless the timer is already short (which it
will be if the Snooper received the first Query). It forwards the Query out all its ports.
8. If the Snooper or Querier receives a Membership Report on a port, it sets the port timer to
the Group Membership Interval value and continues to forward the multicast stream out that
port. Otherwise, the timers for that port expire and the Snooper and/or Querier stops
forwarding the multicast stream out that port.
Querier timer values
As described in Step 3 above, when the Querier sends a Specific Query for a group in response
to a Leave message, the Querier updates a timer for ports that forward that group.
The timer is the following two values multiplied together:

Last Member Query Count (LMQC)—the number of Specific Queries the Querier sends, 2
by default, and

Last Member Query Interval (LMQI)—the time between the Specific Queries, 1 second by
default
The default LMQC and LMQI give a timeout of 2 seconds. Therefore, by default the Querier
must see the client response within 2 seconds of sending the first Specific Query.
Because of this process, sensible values for LMQC and LMQI are essential. In most networks,
the defaults are appropriate and you should not change them. If you need to change them, see
"Last Member Query Count and Last Member Query Interval" on page 71.
The command show ip igmp displays the timer for the most recently updated port as the
group’s Refresh Time.
Page 60 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
How clients leave groups: queries and timers
Snooper timer values
As described in Step 5 above, when the Snooper receives a Specific Query from the Querier, it
may update a timer for ports that forward that group. The following flow chart describes the
decision-making process for updating the timer.
Start:
Switch receives
Query for which
it has a group
entry.
Has the switch
previously seen a
Leave message?
NO
YES
For this
port, is the group
entry dynamic
(not static)?
NO
Do not alter port-specific
group membership timer.
Flood Query out all ports.
YES
Is the port’s
current timer ≥
LMQI from Querier
LMQC from
Snooper?
NO
YES
Set port-specific group
membership timer to:
LMQI from Querier
LMQC from Snooper.
Note that:

The command show ip igmp snooping statistics interface displays the timer for the most
recently updated port as the time displayed in the entry:
Group mode: Exclude (Expires: <time>).

To calculate the timer, the Snooper takes the LMQI value that it receives from the Querier
and multiplies it by the Snooper’s own LMQC.

The Snooper only reduces the timer if it receives a Leave message followed by a Specific
Query—one of the messages is not enough.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 61
IGMP Fast Leave
Comparing the Querier and Snooper timers
By default, the Querier and Snooper port-specific group timers have the same value
(2 seconds). This is because the LMQC is the same for the Querier and the Snoopers.
Consequences for high-loss and high-lag networks
If packet loss or lag time is an issue in your network, we recommend increasing the Robustness
Variable on the Snoopers and the Querier.
On Allied Telesis Snoopers and Queriers, LMQC = Robustness Variable. For Snoopers, not all
vendors make these counters the same. RFC 2236 requires that LMQC and Robustness
Variable have the same value on Queriers, but the IGMP timer rules for IGMP Snoopers are less
well-defined.
Increasing the Querier LMQC (or Robustness Variable) increases the number of Specific
Queries that the Querier sends. This increases the probability that an interested client will
receive a Query.
Increasing the Snooper LMQC (or Robustness Variable) increases the length of time that the
Snooper waits before aging out the port. This gives the client more time to reply to the Queries.
For example, if you increase the LMQC to 5 (the maximum) on the Querier and the Snooper,
then the Querier sends 5 Queries and the Snooper waits for 5 * LMQI, which is 5 seconds with
the default LMQI.
Make sure that the values on the Querier and the Snoopers match, so that the Snooper has
time to forward all the Queries. For example, if you changed the Querier’s Robustness Variable
to 5 but left the Snooper unchanged, the Querier would send out 5 Queries 1 second apart but
the Snooper would age out the group entry after only the first 2 Queries.
For more information about setting the Robustness Variable, and the consequences of this, see
"Robustness Variable" on page 73.
IGMP Fast Leave
IGMP Fast Leave enhances your control over router bandwidth. Enabling Fast Leave tells IGMP
snooping to stop the transmission of a group multicast stream to a port as soon as it receives a
Leave message on that port. No timeouts are observed.
Ordinarily, when IGMP snooping sees a Leave message, it waits for a Membership Query
message before setting the entry timeout to 2 seconds. Fast Leave tells IGMP to drop the entry
from the port as soon as the Leave message is seen. For this reason, Fast Leave should only be
configured on interfaces that have one client per port.
Page 62 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP Fast Leave
This example shows how to enable fast-leave processing on a VLAN.
awplus# configure terminal
awplus(config)# interface vlan1
awplus(config-if)# ip igmp snooping fast-leave
Example
This example uses the same network configuration as the IGMP Snooping "Configuration
Example" on page 10. For convenience, the diagram is reproduced below.
Multicast
Server
port1.0.1
00
x9
port1.0.11
Switch-1:
Querier
port1.0.12
Switch-2:
Snooper
port1.0.11
Switch-3:
Snooper
port1.0.12
port1.0.11
00
x6
00
x6
port1.0.12
(blocked by STP)
port1.0.1
Clie
nt
1
port1.0.1
Clie
nt
2
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 63
IGMP Fast Leave
1. Configure Switch-1.
Switch-1 is an IGMP Querier.
!
hostname Switch-1
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
!
interface vlan100
ip address 192.168.100.254/24
ip igmp
ip igmp version 2
2. Configure Switch-2.
Switch-2 is an IGMP Snooper. IGMP snooping is enabled by default and does not need any
configuration.
!
hostname Switch-2
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
Page 64 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP Fast Leave
3. Configure Switch-3.
Switch-3 is also an IGMP Snooper. Fast leave is enabled on this switch.
!
hostname Switch-3
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
!
interface vlan100
ip igmp snooping fast-leave
Explanation of IGMP Fast Leave
Imagine that Client-2 on Switch-3 sends a Membership Report to join the group 224.12.13.14.
The Snooper, Switch-3, adds this to its IGMP snooping table. When the same client then sends a
Leave message, the IGMP Querier responds with a Membership Query and waits for a
configured time for a response.
The following sections describe in detail the differences between having Fast Leave disabled and
enabled, but in summary:

Without Fast Leave, the IGMP Snooper waits the same length of time as the Querier, then
expires the entry if there was no response.

With Fast Leave, the IGMP Snooper expires the entry as soon as it sees the Leave message
from the client. By the time the Querier sends the Membership Query, the Snooper will have
already expired the entry and therefore stopped sending the stream to the client.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 65
IGMP Fast Leave
When Fast Leave is disabled
The IGMP Snooper sees the Membership Query from the Querier and accordingly sets its
expiry time in seconds to match the Querier.
Switch-3# sh ip igmp int vlan100
Interface vlan100 (Index 400)
IGMP Disabled, Active(Snoop Only), Non-Querier, Version 3 (default)
IGMP interface has 2 group-record states
IGMP activity: 68 joins, 0 leaves
IGMP querying router is 192.168.100.254
IGMP robustness variable is 2
IGMP last member query count is 2
IGMP query interval is 125 seconds
IGMP Startup query interval is 31 seconds
IGMP Startup query count is 2
IGMP query holdtime is 500 milliseconds
IGMP querier timeout is 255 seconds
IGMP max query response time is 10 seconds
Group Membership interval is 260 seconds
IGMP Last member query count is 2
Last member query response interval is 1000 milliseconds
Strict IGMPv3 ToS checking is disabled on this interface
Source Address checking is enabled
IGMP Snooping is globally enabled
IGMP Snooping query solicitation is globally enabled for Root/Master
Nodes
IGMP Snooping query solicitation is globally disabled for Non Root/
Master Nodes
Num. query-solicit packets: 0 sent, 0 recvd
IGMP Snooping is enabled on this interface
IGMP Snooping fast-leave is not enabled
IGMP Snooping querier is not enabled
IGMP Snooping report suppression is enabled
If no Membership Report is received by the time the counters go to zero, then the client's entry
is dropped from both the IGMP Querier and Snooper.
When you enable fast leave on Switch-3
When Fast Leave is enabled on Switch-3, but not on Switch-1, an interesting chain of events
occurs when the client sends a Leave message, as shown in the following diagram.
The result of this is that Switch-3 adds the group back into its snooping table (with the same
timeout as the IGMP Querier) but has no ports interested in receiving the group. Because Fast
Leave is enabled on vlan100, that port was removed from the group as soon as Switch-3
received the Leave message.
Page 66 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP Fast Leave
Switch-3#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Group Type:
Router Port Learnt
Interface:
vlan100
Group:
224.0.0.2
Uptime:
02:24:16
Group mode:
Include ()
Last reporter: 192.168.100.254
Port member list:
port1.0.12 - 135 secs
Interface:
vlan100
Group:
224.12.13.14
Flags:
Uptime:
00:12:23
Group mode:
Exclude (Expires: 00:02:19)
Last reporter: 192.168.100.20
Source list is empty
Port member list:
port1.0.1 - 140 secs
We can see the entry for 224.12.13.14 with port 1.0.1 associated with this entry. Now we send
a Leave message from the client attached to port 1.0.1, and with Fast Leave enabled on vlan100
the switch now removes the port association while keeping the entry in the table as an
unregistered group.
Switch-3#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Group Type:
Router Port Learnt
Interface:
vlan100
Group:
224.0.0.2
Uptime:
02:24:30
Group mode:
Include ()
Last reporter: 192.168.100.254
Port member list:
port1.0.12 - 258 secs
Group Type:
Interface:
Group:
Uptime:
Group mode:
Last reporter:
UnReg MC Group
vlan100
224.12.13.14
00:00:03
Include (Expires: 00:04:16)
192.168.1.100
Adding Fast Leave to Switch-1 would not be sensible, since there may be clients attached to
other ports on Switch-3. If you enabled Fast Leave on Switch-1, one Leave message from
Switch-3 would drop the multicast stream for everyone on that switch.
It is safe to ignore the group entry on Switch-3.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 67
Configurable IGMP timers and counters
Immediate Leave and Fast Leave
Both Layer 2 IGMP Immediate Leave and Layer 3 IGMP Snooping Fast Leave are enabled on a
per interface basis.
The following example shows how to enable the Immediate Leave feature on the VLAN
interface vlan2 for a specific range of multicast groups.
Configure IGMP Immediate Leave:
awplus# configure terminal
awplus(config)# access-list 34 permit 225.192.20.0 0.0.0.25
awplus(config)# interface vlan2
awplus(config-if)# ip igmp immediate-leave group-list 34
awplus(config-if)# exit
Configure IGMP Snooping Fast Leave:
awplus(config)# int vlan2
awplus(config-if)# ip igmp snooping fast-leave
awplus(config-if)# exit
awplus(config)# sh run int vlan2
!
interface vlan2
ip igmp snooping fast-leave
!
Configurable IGMP timers and counters
This section looks at some of the timers and counters that control how often IGMP sends
queries and how quickly entries time out. First, it gives background information in the following
subsections:
z
"Timer and counter relationships" on page 69
z
"Default values" on page 70
Then it looks at each of the configurable timers and counters, in the following subsections:
z
"Last Member Query Count and Last Member Query Interval" on page 71
z
"Robustness Variable" on page 73
z
"Default Query Interval" on page 75
z
"Max Query Response Interval" on page 76
z
"Group Membership Interval" on page 78
Page 68 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Configurable IGMP timers and counters
RFC 2236 also describes other counters and timers that this section does not describe, because
this section only describes the counters and timers that you can directly set. The switch derives
other counters and timers from the above subset.
Timer and counter relationships
The above timers and counters are related to each other and to others in RFC 2236 by the
following formulae:

Last Member Query Count = Robustness Variable

Group Membership Interval = (Robustness Variable * Default Query Interval) +
one Query Response Interval in seconds

Startup Query Count = Robustness Variable
The Startup Query Count is the number of General Queries that the Querier sends when
it starts up.

Other Querier Timeout = (Robustness Variable * Default Query Interval) +
(Query Response Interval in seconds/2)
The Other Querier Timeout is the length of time that a potential Querier waits after receiving
a Query before it assumes that it should become the Querier.
These relationships mean you need to take care if you change timers or counters. "Example of
bad choices for timer values" on page 78 describes the consequences of a bad combination of
values.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 69
Configurable IGMP timers and counters
Default values
To display the values of the configurable IGMP settings for a VLAN, use the command:
awplus# show ip igmp int vlan<vid>
The following output shows the default values.
Switch-1#show ip igmp int vlan100
Interface vlan100 (Index 400)
IGMP Enabled, Active, Querier, Configured for version 2
Internet address is 192.168.100.254
IGMP interface has 2 group-record states
IGMP activity: 1932 joins, 8 leaves
IGMP robustness variable is 2
IGMP last member query count is 2
IGMP query interval is 125 seconds
IGMP Startup query interval is 31 seconds
IGMP Startup query count is 2
IGMP query holdtime is 500 milliseconds
IGMP querier timeout is 255 seconds
IGMP max query response time is 10 seconds
Last member query response interval is 1000 milliseconds
Group Membership interval is 260 seconds
IGMP Last member query count is 2
Strict IGMPv3 ToS checking is disabled on this interface
Source Address checking is enabled
IGMP Snooping is globally enabled
IGMP Snooping query solicitation is globally enabled for Root/Master
Nodes
IGMP Snooping query solicitation is globally disabled for Non Root/
Master Nodes
Num. query-solicit packets: 0 sent, 0 recvd
IGMP Snooping is enabled on this interface
IGMP Snooping fast-leave is not enabled
IGMP Snooping querier is not enabled
IGMP Snooping report suppression is enabled
All changes are made on the VLAN interface in which the user wants to make the changes.
Page 70 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Configurable IGMP timers and counters
Switch-1(config)#int vlan100
Switch-1(config-if)#ip igmp ?
access-group
IGMP group access group
immediate-leave
Leave groups immediately without
sending last member query, use for one
host network only
last-member-query-count
Last Member Query Count
last-member-query-interval Last Member Query Interval
limit
IGMP Limit
mroute-proxy
Mroute to IGMP proxy
proxy-service
Enable IGMP mroute proxy service
querier-timeout
IGMP previous querier timeout
query-holdtime
Query Hold Time
query-interval
Query Interval
query-max-response-time
IGMP Max Query Response Time
ra-option
IGMP Strict RA Option Validation
robustness-variable
Robustness Variable
snooping
Layer 2 Snooping
source-address-check
Enforce report source address checking
startup-query-count
Startup Query count
startup-query-interval
Startup Query Interval
static-group
Static Group to be Joined
v3toscheck
IGMPv3 strict IP ToS checking (0xC0)
version
IGMP Version
Note that units for Last Member Query Interval (LMQI) and Query Response Interval are
.001seconds (i.e., milliseconds). Therefore, the default LMQI of 1 second is shown as 1000ms
The units for the Max Query Response Interval are seconds. The default Max Query Response
Interval is 10 seconds.
Last Member Query Count and Last Member Query Interval
The Last Member Query Count (LMQC) is the number of Specific Queries the Querier sends
after receiving a Leave message—1 to 5 messages.
The Last Member Query Interval (LMQI) is the time between the Specific Queries—1000 to
25500 in units of 0.001 seconds.
These counters determine how quickly a group times out when the last client leaves the group.
You should read this section in conjunction with "How clients leave groups: queries and
timers" on page 59, which has an outline of the leave process and a detailed discussion of the
timers.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 71
Configurable IGMP timers and counters
What these counters do
On the Querier and all Snoopers, IGMP keeps group membership timeout values on each port.
During general multicasting, these timeouts are (by default) 260 seconds. When a client leaves a
group, these timeouts are reduced to make multicasting stop quickly after the last client leaves.
The LMQC and LMQI determine the value of the timeout during this leave process (2 seconds
with the default LMQC and LMQI).
On the Querier:
timeout during the leave process = LMQC * LMQI
On Snoopers:
timeout during the leave process = LMQI from Querier * LMQC from Snooper
The command show ip igmp interface vlan displays the timers for a particular interface.
Potential problems with changing these counters
For most networks, the default LMQI and LMQC values work. You should only change them if
you are aware of the likely effect on the network. In particular, note that:

Changing the LMQC automatically changes the Robustness Variable. Therefore, we do not
recommend setting the LMQC to 1, because it removes the system’s allowance for packet
loss. See "Robustness Variable" on page 73 for more information about the consequences of
changing the Robustness Variable.

If you set the LMQI (or LMQC, or both) too low, clients will not be able to reply to Specific
Queries quickly enough and the Querier and Snoopers may delete group entries for ports
that still need to receive multicasts. If this happens, some or all clients briefly lose the multicast
stream.

The default values of LMQI (1000ms) and LMQC (2) mean that the Querier must receive
client Membership Reports within 2 seconds of the first Query. This is already quite a short
time and we do not recommend reducing it even more. For example, reducing the LMQI to
500ms would allow only one second for responses, which may be too little.
How to change these counters
The following example increases LMQI a lot, and then shows the resulting changed refresh time.
Switch-1#conf t
Switch-1(config)#int vlan100
Switch-1(config-if)#ip igmp last-member-query-interval ?
<1000-25500>
ms)
Last Member Query Interval value (Default: 1000
Switch-1(config-if)#ip igmp last-member-query-interval 255
Page 72 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Configurable IGMP timers and counters
Switch-1#show ip igmp int vlan100
Interface vlan100 (Index 400)
IGMP Enabled, Active, Querier, Configured for version 2
Internet address is 192.168.100.254
IGMP interface has 2 group-record states
IGMP activity: 1966 joins, 8 leaves
IGMP robustness variable is 2
IGMP last member query count is 2
IGMP query interval is 125 seconds
IGMP Startup query interval is 31 seconds
IGMP Startup query count is 2
IGMP query holdtime is 500 milliseconds
IGMP querier timeout is 255 seconds
IGMP max query response time is 10 seconds
Last member query response interval is 255 milliseconds
Group Membership interval is 260 seconds
IGMP Last member query count is 2
Strict IGMPv3 ToS checking is disabled on this interface
Source Address checking is enabled
IGMP Snooping is globally enabled
IGMP Snooping query solicitation is globally enabled for Root/Master Nodes
IGMP Snooping query solicitation is globally disabled for Non Root/Master Nodes
Num. query-solicit packets: 0 sent, 0 recvd
IGMP Snooping is enabled on this interface
IGMP Snooping fast-leave is not enabled
IGMP Snooping querier is not enabled
IGMP Snooping report suppression is enabled
The refresh time in seconds is (LMQI/1000) * LMQC = 255/1000 * 2 = 0.5 seconds
Robustness Variable
What this counter does
The Robustness Variable (RV) allows you to tune for the expected packet loss on a subnet. If
you expect a subnet to be lossy, you can increase the RV. IGMP is robust to packet loss of one
packet less than the RV. The RV is an integer from 1 to 5 and should not be set to 1.
If packet loss or lag time is an issue in your network, we recommend increasing the Robustness
Variable on the Snoopers and the Querier. This increases the following:

the number of Queries that the Querier sends out (by increasing the LMQC)

the amount of time that the Querier and the Snoopers wait for clients to reply
For more details, see "Consequences for high-loss and high-lag networks" on page 62.
Potential problems with changing this counter
The RV is the counter you are most likely to need to change. However, you need to appreciate
the effect this has on your network, as described in RFC 2236. Changing the RV changes other
values from the RFC, as follows:

Last Member Query Count = Robustness Variable
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 73
Configurable IGMP timers and counters

Group Membership Interval = (Robustness Variable * Default Query Interval) + one Query
Response Interval in seconds

Startup Query Count = Robustness Variable

Other Querier Timeout = (Robustness Variable * Default Query Interval) + (Query
Response Interval in seconds/2)
The Group Membership Interval automatically changes to match the above formula.

Group Membership Interval = (Robustness Variable * Default Query Interval) +
one Query Response Interval in seconds
How to change this counter
Switch-1# conf t
Enter configuration commands, one per line.
End with CNTL/Z.
Switch-1(config)# int vlan100
Switch-1(config-if)# ip igmp robustness-variable ?
<1-7>
Robustness Variable value (Default: 2)
Switch-1(config-if)# ip igmp robustness-variable 5
Note that the Last Member Query Count, Startup Query Count, Group Membership Interval
and Last Member Query Count have also changed.
Switch-1#sh ip igmp int vlan100
Interface vlan100 (Index 400)
IGMP Enabled, Active, Querier, Configured for version 2
Internet address is 192.168.100.254
IGMP interface has 3 group-record states
IGMP activity: 18 joins, 0 leaves
IGMP robustness variable is 5
IGMP last member query count is 5
IGMP query interval is 125 seconds
IGMP Startup query interval is 31 seconds
IGMP Startup query count is 5
IGMP query holdtime is 500 milliseconds
IGMP querier timeout is 630 seconds
IGMP max query response time is 10 seconds
Last member query response interval is 1000 milliseconds
Group Membership interval is 635 seconds
IGMP Last member query count is 5
Strict IGMPv3 ToS checking is disabled on this interface
Source Address checking is enabled
IGMP Snooping is globally enabled
IGMP Snooping query solicitation is globally enabled for Root/Master
Nodes
IGMP Snooping query solicitation is globally disabled for Non Root/
Master Nodes
Num. query-solicit packets: 0 sent, 0 recvd
IGMP Snooping is enabled on this interface
IGMP Snooping fast-leave is not enabled
IGMP Snooping querier is not enabled
IGMP Snooping report suppression is enabled
Page 74 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Configurable IGMP timers and counters
Default Query Interval
What this timer does
To maintain an accurate picture of group membership, the Querier periodically sends General
Queries to all its IGMP interfaces. The Default Query Interval is the gap between General
Queries.
Note that General Queries are quite different from Specific Queries, which the Querier sends
to a group address when it receives a Leave message for that group.
The router only sends General or Specific Queries if it is the Querier. If another router is elected
as the Querier, the non-elected router ignores the Default Query Interval and other such
settings.
Potential problems with changing this timer
If you change the Default Query Interval, the Group Membership Interval also needs to change
so that clients have an appropriate amount of time to reply to the Query.
How to change this timer
The Default Query Interval is an integer from 1 to 65535 seconds, specified using the
query-interval parameter. The default is 125 seconds. The following example tweaks the
interval. Note that the IGMP Querier timeout and Group Membership Interval also change.
Switch-1#conf t
Switch-1(config)#int vlan100
Switch-1(config-if)#ip igmp quer
Switch-1(config-if)#ip igmp query-interval ?
<2-18000>
Query Interval value (Default: 125 s)
Switch-1(config-if)#ip igmp query-interval 120
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 75
Configurable IGMP timers and counters
Switch-1#sh ip igmp int vlan100
Interface vlan100 (Index 400)
IGMP Enabled, Active, Querier, Configured for version 2
Internet address is 192.168.100.254
IGMP interface has 3 group-record states
IGMP activity: 16 joins, 0 leaves
IGMP robustness variable is 2
IGMP last member query count is 2
IGMP query interval is 120 seconds
IGMP Startup query interval is 31 seconds
IGMP Startup query count is 2
IGMP query holdtime is 500 milliseconds
IGMP querier timeout is 245 seconds
IGMP max query response time is 10 seconds
Last member query response interval is 1000 milliseconds
Group Membership interval is 250 seconds
IGMP Last member query count is 2
Strict IGMPv3 ToS checking is disabled on this interface
Source Address checking is enabled
IGMP Snooping is globally enabled
IGMP Snooping query solicitation is globally enabled for Root/Master
Nodes
IGMP Snooping query solicitation is globally disabled for Non Root/
Master Nodes
Num. query-solicit packets: 0 sent, 0 recvd
IGMP Snooping is enabled on this interface
IGMP Snooping fast-leave is not enabled
IGMP Snooping querier is not enabled
IGMP Snooping report suppression is enabled
Max Query Response Interval
What this timer does
The Max Query Response Interval determines the longest time clients can take to reply to a
General Query. The Querier inserts the Max Query Response Interval into General Query
messages. Clients randomly choose a time between 0 and the Max Query Response Interval at
which to respond to a General Query. Increasing the Query Response Interval spreads IGMP
messages over a longer time period, which reduces the burstiness of traffic on the network.
It may be useful to decrease the Max Query Response Interval if you are running EPSR or RSTP.
Decreasing the Max Query Response Interval reduces the recovery time after a topology
change. For more information, see "Query solicitation (rapid recovery from topology
changes)" on page 34.
Potential problems with changing this timer
If your network has many multicast clients and you make the Max Query Response Interval too
short, you may congest the Snoopers and Querier with too many Report messages in a short
time.
If you change the Max Query Response Interval, the Group Membership Interval also needs to
change, so that clients have an appropriate amount of time to reply to the Query.
Page 76 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Configurable IGMP timers and counters
How to change this timer
The Max Query Response Interval is an integer from 1 to 3180 seconds, specified using the
query-max-response-time parameter. The default is 10 seconds.
Switch-1# conf t
Switch-1(config)# int vlan100
Switch-1(config-if)# ip igmp query-max-response-time ?
<1-3180>
Query Reponse Time (Default: 10 s)
Switch-1(config-if)#ip igmp query-max-response-time 100
Switch-1#sh ip igmp int vlan100
Interface vlan100 (Index 400)
IGMP Enabled, Active, Querier, Configured for version 2
Internet address is 192.168.100.254
IGMP interface has 3 group-record states
IGMP activity: 12 joins, 0 leaves
IGMP robustness variable is 2
IGMP last member query count is 2
IGMP query interval is 125 seconds
IGMP Startup query interval is 31 seconds
IGMP Startup query count is 2
IGMP query holdtime is 500 milliseconds
IGMP querier timeout is 300 seconds
IGMP max query response time is 100 seconds
Last member query response interval is 1000 milliseconds
Group Membership interval is 350 seconds
IGMP Last member query count is 2
Strict IGMPv3 ToS checking is disabled on this interface
Source Address checking is enabled
IGMP Snooping is globally enabled
IGMP Snooping query solicitation is globally enabled for Root/Master
Nodes
IGMP Snooping query solicitation is globally disabled for Non Root/
Master Nodes
Num. query-solicit packets: 0 sent, 0 recvd
IGMP Snooping is enabled on this interface
IGMP Snooping fast-leave is not enabled
IGMP Snooping querier is not enabled
IGMP Snooping report suppression is enabled
In this example, the Querier sends a General Query every 125 seconds. The General Query
contains the Max Query Response Interval of 100, which tells clients that they have 100 seconds
to reply to this General Query message.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 77
Example of bad choices for timer values
Group Membership Interval
What this timer does
The Group Membership Interval specifies the length of time before the switch deletes a group
from its multicast group database after the switch last receives a Membership Report for that
group. All IGMP routers and switches in a network use this interval to maintain their group
membership databases, not just the Querier.
The Querier also uses this interval to close down multicasting if it receives no replies to all
General Queries for a group. If the Querier sends a General Query and does not receive any
Membership Reports in response, it continues to send any existing multicast streams. In the
meanwhile, the Group Membership Interval counts down until it hits zero, at which point the
Querier stops propagating the multicast streams through the LAN.
Potential problems with changing this timer
Making the Group Membership Interval too short has serious consequences. You remove the
network's ability to cope with losing a General Query and you may not give enough time for
client responses to reach the Querier. These problems would cause multicasting to stop for
some or all clients. For more information, see "Example of bad choices for timer values" on
page 78.
Synchronisation of timers
The Group Membership Interval is a function of several other timers, according to the following
formula from RFC 2236:
Group Membership Interval =
(Robustness Variable * Default Query Interval) + one Query Response Interval in seconds
The Group Membership Interval changes automatically if you change either the Robustness
Variable or the Query Response Interval.
Example of bad choices for timer values
It is generally unwise to change any of the default IGMP settings unless you have advanced
knowledge of how IGMP works. As "Timer and counter relationships" on page 69 describes,
most of the timers and counters are related. This means setting timers can cause problems
unless you understand the potential impact on the IGMP process.
This example sets three timers to excessively short values and discusses the potential
consequences.
Page 78 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Example of bad choices for timer values
Example
Imagine the following changes to the configuration:
TIMER PARAMETER
NEW PARAMETER VALUE
Last Member Query Interval
0.5 seconds
Max Query Response Interval
1
Query Interval
126
The commands to configure these settings are:
Switch-1(config-if)# ip igmp last-member-query-interval 500
Switch-1(config-if)# ip igmp query-max-response-time 1
Switch-1(config-if)# ip igmp query-interval 126
The resulting values are displayed in the following output.
Switch-1#sh ip igmp int vlan100
Interface vlan100 (Index 400)
IGMP Enabled, Active, Querier, Configured for version 2
Internet address is 192.168.100.254
IGMP interface has 2 group-record states
IGMP activity: 193 joins, 1 leaves
IGMP robustness variable is 2
IGMP last member query count is 2
IGMP query interval is 126 seconds
IGMP Startup query interval is 31 seconds
IGMP Startup query count is 2
IGMP query holdtime is 500 milliseconds
IGMP querier timeout is 254 seconds
IGMP max query response time is 5 seconds
Last member query response interval is 5000 milliseconds
Group Membership interval is 257 seconds
IGMP Last member query count is 2
Strict IGMPv3 ToS checking is disabled on this interface
Source Address checking is enabled
IGMP Snooping is globally enabled
IGMP Snooping query solicitation is globally enabled for Root/Master
Nodes
IGMP Snooping query solicitation is globally disabled for Non Root/
Master Nodes
Num. query-solicit packets: 0 sent, 0 recvd
IGMP Snooping is enabled on this interface
IGMP Snooping fast-leave is not enabled
IGMP Snooping querier is not enabled
IGMP Snooping report suppression is enabled
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 79
Stopping Snoopers from snooping non-IGMP messages
Problem 1: Last Member Query Interval too short
The Last Member Query Interval was set to 500ms, using the command:
Switch-1(config-if)# ip igmp last-member-query-interval 500
This value is very low—half a second. A Last Member Query Count of 2 (the default), gives
your clients 1 second to get their Report back to the Querier before the Snooper and Querier
stop sending the data stream. Using too low a Last Member Query Interval may mean that
some or all clients briefly lose the multicast stream.
Problem 2: Query Response Interval short
The Query Response Interval was also set to 5 tenths of a second, using the command:
awplus(config-if)# ip igmp query-interval 5
This value is also half a second. This value means that clients randomly pick a time between 0
and 0.5 seconds to respond (send a Report) to a Query. Using a short time here congests the
Snoopers and Querier with Reports in a short space of time. This is not necessarily a problem if
you only have a few clients, but 0.5 seconds is definitely a short window of time.
Stopping Snoopers from snooping non-IGMP
messages
Some networks include routers that have no interest in IGMP, but still generate multicast
messages by running protocols like OSPF. When a Snooper receives multicast messages from
such a router, the Snooper adds the router's port to its All Groups port list. This means the
router is unnecessarily sent IGMP and multicast traffic. Using IGMP features to prevent the
excess traffic is particularly helpful when you cannot or do not want to control the traffic at the
router.
This example describes how to use AlliedWare Plus’ advanced IGMP features to prevent this
behaviour, by limiting the ports that the Snooper adds to the All Groups list, or by stopping
particular types of traffic from adding ports to the All Groups list.
Page 80 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Stopping Snoopers from snooping non-IGMP messages
Example
The example is based around a network that has a router running OSPF. The router is
connected to a LAN through a switch. The LAN is a single subnet with no OSPF routers inside
it. The network for this example uses the same loop as for "IGMP snooping" on page 8, with a
router attached to Switch-2. The network is shown in the following figure.
Multicast
Server
port1.0.1
00
x9
port1.0.11
Switch-1:
Querier
port1.0.12
OSPF
OSPF
Switch-2:
Snooper
Switch-3:
Snooper
port1.0.12
port1.0.11
port1.0.11
00
00
x6
x6
port1.0.12
port1.0.24
(blocked by STP)
port1.0.3
port1.0.2
Clie
nt
1
OSPF
Clie
nt
2
88
24
Router
We used an AT-8824 switch running AlliedWare for the Router in this example.
Each example in this section modifies the following base configuration.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 81
Stopping Snoopers from snooping non-IGMP messages
Switch-1 Configuration—IGMP Querier
!
hostname Switch-1
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
vlan 100 state enable
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
!
interface vlan100
ip address 192.168.100.254/24
ip igmp
ip igmp version 2
Switch-2 Configuration—IGMP Snooper
!
hostname Switch-2
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
vlan 100 state enable
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
Page 82 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Stopping Snoopers from snooping non-IGMP messages
Switch-3 Configuration—IGMP Snooper
!
hostname Switch-3
!
spanning-tree mode rstp
!
vlan database
vlan 100 name vlan100
vlan 100 state enable
!
interface port1.0.1-1.0.10
switchport access vlan 100
spanning-tree edgeport
!
interface port1.0.11-1.0.12
switchport
switchport mode access
switchport access vlan 100
!
interface port1.0.13-1.0.24
switchport access vlan 100
spanning-tree edgeport
Router Configuration—OSPF
set system name=Router
# VLAN general configuration
create vlan=vlan100 vid=100
add vlan=100 port=1-4
create vlan=vlan2 vid=2
add vlan=2 port10-12
# IP configuration
enable ip
set ip autonomous=65000
add ip int=vlan100 ip=192.168.100.100 mask=255.255.255.0
add ip int=vlan2 ip=10.0.0.1
# OSPF configuration
set ospf routerid=192.168.100.100
add ospf area=0.0.0.1
add ospf range=192.168.100.0 area=0.0.0.1 mask=255.255.255.0
add ospf interface=vlan100 area=0.0.0.1
enable ospf
With the configuration above, the router sends OSPF messages to Switch-2. As the following
outputs show, this means that:

Switch-2 designates port 1.0.11 and 1.0.24 as the Router ports.

Switch-2 forwards the OSPF packets to port 1.0.11 on Switch-1, so Switch-1 designates
port1.0.11 as the Router port.

Switch-3 forwards the OSPF packets to uplink port 1.0.12 on Switch-1, so Switch-1
designates port1.0.12 as a Router port.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 83
Stopping Snoopers from snooping non-IGMP messages
Switch-1# sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Group Type:
Router Port Learnt
Interface:
vlan100
Group:
224.0.0.2
Uptime:
00:07:07
Group mode:
Include ()
Last reporter: 192.168.100.100
Port member list:
port1.0.12 - 250 secs
Switch-2 has two entries for the Router Port: port1.0.12, which is connected to Switch-1—the
IGMP Querier—and port1.0.24, which has the OSPF router connected to it.
Switch-2#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Group Type:
Router Port Learnt
Interface:
vlan100
Group:
224.0.0.2
Uptime:
00:16:09
Group mode:
Include ()
Last reporter: 192.168.100.100
Port member list:
port1.0.24 - 251 secs
port1.0.12 - 215 secs
On Switch-3, the Router port is learnt on interface port1.0.12
Switch-3#sh ip igmp snooping statistics interface vlan100
IGMP Snooping statistics for vlan100
Group Type:
Router Port Learnt
Interface:
vlan100
Group:
224.0.0.2
Uptime:
00:08:32
Group mode:
Include ()
Last reporter: 192.168.100.100
Port member list:
port1.0.12 - 250 secs
Page 84 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Stopping Snoopers from snooping non-IGMP messages
Controlling which addresses create All Groups entries
The router or switch adds a port to its All Groups list when it determines that the port has a
router attached to it. This example shows how to influence the switch's process in determining
who is a router, and therefore when to add a port to the All Groups list.
You can control the criteria for deciding which packets actually indicate the presence of a router
on a particular port, by using the command:
awplus(config-if)# ip igmp snooping routermode {all|default|ip|
multicastrouter|address <ip-address>}
With this command, you specify (in effect) a list of IP addresses. When the switch receives a
multicast packet on a port, it compares the packet's destination IP address with the list. If they
match, the switch considers the packet to be from a "router", and adds the port to the All
Groups list.
The following table shows the address lists that each command option gives.
THIS OPTION...
MEANS THAT THE PORT IS TREATED AS A MULTICAST ROUTER PORT IF
IT RECEIVES PACKETS FROM...
all
any reserved multicast addresses (224.0.0.1 to 224.0.0.255)
default
224.0.0.1 (IGMP Queries)
224.0.0.2 (all routers on this subnet)
224.0.0.4 (DVMRP routers)
224.0.0.5 (all OSPFIGP routers)
224.0.0.6 (OSPFIGP designated routers)
224.0.0.9 (RIP2 routers)
224.0.0.13 (all PIM routers)
224.0.0.15 (all CBT routers)
multicastrouter
224.0.0.4 (DVMRP routers)
224.0.0.13 (all PIM routers)
ip
the current list of addresses,
plus addresses specified using the command ip igmp snooping
routermode address,
minus addresses specified using the command no ip igmp snooping
routermode address.
Switch-2# sh ip igmp snooping routermode
Router mode.............IP
Reserved multicast address
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 85
IGMP debugging
IGMP debugging
In this section, we shall examine the debugging messages that the switch outputs when certain
events occur while debugging is enabled. To enable debugging, use the command:
awplus# debug igmp {all|decode|encode|events|fsm|tib}
Switch-1# debug igmp ?
all
Turn on all Debugging
decode IGMP decode
encode IGMP encode
events IGMP events
fsm
IGMP FSM
tib
IGMP Tree-Info-Base (TIB)
PARAMETER
MEANING
all
Enable or disable all debug options for IGMP
decode
Debug of IGMP packets that have been received
encode
Debug of IGMP packets that have been sent
events
Debug IGMP events
fsm
Debug IGMP Finite State Machine (FSM)
tib
Debug IGMP Tree Information Base (TIB)
A client joins a group
Client 2 sends a Membership Report for group 224.12.13.14. Switch-1 sees the report on
vlan100 (1.0.11), and adds the port to its IGMP and IGMP snooping tables. In this example we
will show this using the following debugging options:
debug igmp decode
debug igmp events
Switch-1#19:52:20 Switch-1 IMISH[26241]: debug igmp decode
19:52:25 Switch-1 NSM[1257]: [IGMP-DECODE] : IP packet 192.168.100.100->224.0.0.5 on
vlan100(port1.0.11) triggers router port detection
19:52:25 Switch-1 NSM[1257]: [IGMP-DECODE] : UnReg Grp 224.12.13.14 on vlan100
19:52:34 Switch-1 NSM[1257]: [IGMP-DECODE] : IGMP V2 Membership Report, (Src=0.0.0.0)
Max. Rsp. Code 0 on port1.0.11
19:52:34 Switch-1 NSM[1257]: [IGMP-DECODE] : Grp 224.12.13.14 on vlan100
Switch-1#term mon
Switch-1#debug igmp events
Page 86 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
IGMP debugging
19:59:05 Switch-1 IMISH[2155]: debug igmp events
19:59:15 Switch-1 NSM[1260]: [IGMP-EVENTS] : Deleting Unreg MC
vlan100
19:59:15 Switch-1 NSM[1260]: [IGMP-EVENTS] : Grp Timer Refresh
vlan100(port1.0.11)
19:59:16 Switch-1 NSM[1260]: [IGMP-EVENTS] : Expiry (Host-Side
Timer) for 224.12.13.14 on vlan100
19:59:17 Switch-1 NSM[1260]: [IGMP-EVENTS] : Expiry (Host-Side
Timer) for 224.12.13.14 on vlan100
19:59:21 Switch-1 NSM[1260]: [IGMP-EVENTS] : Exipry on vlan100
19:59:22 Switch-1 NSM[1260]: [IGMP-EVENTS] : Grp Timer Refresh
vlan100(port1.0.11)
Grp 224.12.13.14 on
224.12.13.14 on
Generate Grp Report
Generate Grp Report
224.12.13.14 on
A client leaves a group
Client 2 sends a Leave message for group 224.12.13.14. Switch-1 sees the Leave message on
vlan100 (1.0.11).
Switch-1#19:52:20 Switch-1 IMISH[26241]: debug igmp decode
20:04:25 Switch-1 NSM[1260]: [IGMP-DECODE] : IGMP V2 Membership Report, (Src=0.0.0.0)
Max. Rsp. Code 0 on port1.0.11
20:04:25 Switch-1 NSM[1260]: [IGMP-DECODE] : Grp 224.12.13.14 on vlan100
20:04:25 Switch-1 NSM[1260]: [IGMP-DECODE] : IP packet 192.168.100.100->224.0.0.5 on
vlan100(port1.0.11) triggers router port detection
20:04:33 Switch-1 NSM[1260]: [IGMP-DECODE] : IGMP V2 Leave Group, (Src=0.0.0.0) Max.
Rsp. Code 0 on port1.0.11
20:04:33 Switch-1 NSM[1260]: [IGMP-DECODE] : Grp 224.12.13.14 on vlan100
20:04:35 Switch-1 NSM[1260]: [IGMP-DECODE] : UnReg Grp 224.12.13.14 on vlan100
We can see the Membership Report for group 224.12.13.14 on port1.0.11, without a source IP
address. And then we can see the Leave received on port 1.0.11.
Switch-1# term mon
Switch-1# debug igmp events
Switch-1#20:02:32 Switch-1 NSM[1260]: [IGMP-EVENTS] : Grp Timer Refresh 224.12.13.14
on vlan100(port1.0.11)
20:02:44 Switch-1 NSM[1260]: [IGMP-EVENTS] : Grp Timer Refresh 224.12.13.14 on
vlan100(port1.0.11)
20:02:45 Switch-1 NSM[1260]: [IGMP-EVENTS] : Expiry (Group Query Re-Transmit Timer)
for Grp 224.12.13.14 on vlan100
20:02:46 Switch-1 NSM[1260]: [IGMP-EVENTS] : Expiry (Group Liveness Timer) for Grp
224.12.13.14 on vlan100
20:02:46 Switch-1 NSM[1260]: [IGMP-EVENTS] : Expiry (L2 IF Grp Liveness Timer) for
Grp 224.12.13.14 on vlan100(port1.0.11)
20:02:46 Switch-1 NSM[1260]: [IGMP-EVENTS] : Setting Grp 224.12.13.14 on
vlan100(port1.0.11) to not dynamic/not static
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 87
Support for IGMPv3
Support for IGMPv3
AlliedWare Plus supports IGMP version 3. What version 3 adds to the IGMP protocol is
support for source-filtering. This means it now supports the ability for users to report interest in
receiving a particular multicast stream only from a specific source or multiple source addresses.
The desired source addresses can be expressed as either:

Please send me the group A.B.C.D from any of the following source addresses (Include
mode), or

Please send me the group A.B.C.D from any source address except the following (Exclude
mode)
This information can be used by multicast routing protocols to avoid delivering the multicast
packets from specific sources to networks where there are no hosts interested in these multicast
streams. This feature is also called Source Specific Multicast (SSM).
AlliedWare Plus IGMPv3 is based on the IETF RFC 3376. IGMPv3 supports two types of
protocol messages:

Membership query messages

Membership report messages
An IGMPv3 Querier can query three types of information using a query message:

A general query to determine the multicast reception state (membership information)
associated with its neighboring hosts’ interfaces for all multicast groups enabled at the
interface.

A group-specific query to determine the multicast reception state for a specific multicast
group associated with its neighboring host's interfaces.

A group-and-source-specific query to determine the multicast reception state for a specific
multicast group and a specified set of sources, associated with its neighboring host's interfaces.
The first two types of query are equivalent to IGMPv2 queries. But the third type of query (The
group-and-source-specific query) is a new type that is introduced by IGMPv3
In IGMPv3, when a client has sent a general query, it is sent with an IP destination address of
224.0.0.1— this is the all-systems multicast address. Group-Specific and Group-and-SourceSpecific Queries are sent with an IP destination address equal to the multicast address of
interest.
At this point we need to point out that there is no such thing as an IGMPv3 leave message. A
host leaves by requesting to receive a group from no sources.
A single IGMPv3 report can contain multiple Group Records. What this means is that the report
can update a host's membership of multiple multicast groups. When the IGMPv3 reports are
sent from the host, they are sent with a destination address of 224.0.0.22. This results in all
IGMPv3 multicast-aware routers listening to the reports.
A system that is operating in IGMPv1 or IGMPv2 compatibility modes sends version 1 or version
2 reports to the multicast group specified in the Group Address field of the Report.
Page 88 | Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™
Support for IGMPv3
An implementation of IGMPv3 must also support the following three message types, for interoperation with previous versions of IGMP:

Version 1 Membership Report [RFC1112]

Version 2 Membership Report [RFC2236]

Version 2 Leave Group [RFC2236]
Benefits
The benefits of using IGMPv3 over IGMPv1 and IGMPv2 include:

Optimized bandwidth utilization: a receiver may request to receive traffic only from explicitly
known sources

Improved security (no denial of service attacks from unknown sources)

Enables service providers to receive content from multiple content providers without
needing to be concerned if the content providers are using overlapping group addresses
Report suppression
The switch can suppress IGMP versions 1 and 2 reports when IGMPSNOOPING is configured.
Report suppression stops reports being sent to an upstream multicast router port when there
are already downstream ports for the requested group on the same downstream VLAN
interface. This reduces the amount of IGMP traffic that is sent to the Querier
Report suppression does not apply to IGMPv3. This functionality is enabled by default for
IGMPv1 and IGMPv2 reports.
The command below enables report suppression for IGMPv2 reports on vlan3, if it has been
disabled.
awplus# conf t
awplus(config)# int vlan3
awplus(config-if)# ip igmp version 2
awplus(config-if)# ip igmp snooping report-suppression
When Client A in vlan3 sends a report to join the group 225.1.2.3, the switch sends this report
upstream to the Querier. If Client B in the same VLAN sends a report for the same multicast
group 225.1.2.3, the switch does not need to forward this report on to the Querier—it had
already done so when receiving the report from Client A.
The switch does not drop the report. It processes the second report to update (refresh) the
liveness timer of the group in its group database, and then not forward it.
When the first client sends a leave message, the switch does not pass the leave message on up
to the Querier because report suppression is on. As a result, the client will continue to receive
traffic until the snooping entry on the port times out, or until the Querier sends a query for this
group and the client does not confirm its membership for the group.
Configure IGMP for Multicasting on Managed Layer 3 Switches on AlliedWare Plus™ | Page 89
When report suppression is enabled, the switch will put its own IP address as the source
address of the reports and leave messages that it sends to the Querier.
When the last client in a group leaves, this causes traffic to stop to all clients straight away (even
to the clients that have already left but are still receiving traffic).
This is simply because a Leave report from the last group member will not be suppressed
(regardless of the suppression setting), but will be immediately forwarded to the Querier, so the
leave sequence is started immediately.
If report suppression is disabled on switches in the network, ensure that immediate leave is not
configured on any switches upstream of those on which report suppression has been disabled.
This is because when report suppression is enabled, the switch will only send a leave upstream if
all of its downstream hosts have left the group, but when report suppression is disabled, all leave
messages received from downstream hosts are simply passed on upstream. If a port upstream of
a suppression-disabled switch is configured for immediate leave, it will stop forwarding the
stream as soon as any downstream host leaves the group, irrespective of whether other
downstream hosts are still members of the group.
Source Address Check
By default AlliedWare Plus only accepts IGMP packets whose source IP address is in the same
subnet as the IP address on the receiving interface. We can override this behaviour using the
command:
Switch-2(config)# int vlan100
Switch-2(config-if)# no ip igmp source-address-check
Tips for making an IGMP network more efficient

Enable Fast Leave—this will cause IGMP snooping to immediately remove group membership
of the port, rather than waiting till the Leave report has gone to the Querier and the Querier
has sent a query in response asking for group membership.

Switch off Report Suppression—this will cause all reports and Leaves from clients to be
immediately forwarded to the Querier, causing the leave sequence to commence straight
away. This is OK if only a small to medium number of clients are connected. Generally, it is
not recommended if there are a very large number of clients, as the Querier will see a lot
more reports than if the edge switches aggregate the reports from the clients.

Move the Querier to the edge switch—this will have the desired effect because the clients
can talk directly with the Querier, however it is not recommended if you have more than one
edge switch.

Reduce the Query Interval on the Querier—this will cause the Querier to send queries more
often and therefore will shorten the time between the client leaving and the general query
C613-16176-00 REV A
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